feat(yamllint): include for this repo and apply rules throughout

* Semi-automated using `ssf-formula` (v0.5.0)
* Fix errors shown below:

```bash
php-formula$ $(grep "\- yamllint" .travis.yml | sed -e "s:^\s\+-\s\(.*\):\1:")
./test/integration/default/inspec.yml
  1:1       warning  missing document start "---"  (document-start)

pillar.example
  3:1       warning  missing document start "---"  (document-start)
  7:22      warning  truthy value should be one of [false, true]  (truthy)
  8:22      warning  truthy value should be one of [false, true]  (truthy)
  10:22     warning  truthy value should be one of [false, true]  (truthy)
  16:17     warning  truthy value should be one of [false, true]  (truthy)
  41:12     error    wrong indentation: expected 10 but found 11  (indentation)
  46:27     warning  truthy value should be one of [false, true]  (truthy)
  70:18     warning  truthy value should be one of [false, true]  (truthy)
  74:19     warning  truthy value should be one of [false, true]  (truthy)
  83:22     warning  truthy value should be one of [false, true]  (truthy)
  97:22     warning  truthy value should be one of [false, true]  (truthy)
  107:89    error    line too long (93 > 88 characters)  (line-length)
  118:20    warning  truthy value should be one of [false, true]  (truthy)
  126:14    error    wrong indentation: expected 12 but found 13  (indentation)
  126:23    warning  truthy value should be one of [false, true]  (truthy)
  151:20    warning  truthy value should be one of [false, true]  (truthy)
  177:19    warning  truthy value should be one of [false, true]  (truthy)
  197:25    warning  truthy value should be one of [false, true]  (truthy)
```

.travis.yml

 ---
 stages:
   - test
-  - commitlint
+  - lint
   - name: release
     if: branch = master AND type != pull_request
 
 
 jobs:
   include:
-    # Define the commitlint stage
-    - stage: commitlint
+    # Define the `lint` stage (runs `yamllint` and `commitlint`)
+    - stage: lint
       language: node_js
       node_js: lts/*
       before_install: skip
       script:
+        # Install and run `yamllint`
+        - pip install --user yamllint
+        # yamllint disable-line rule:line-length
+        - yamllint -s . .yamllint pillar.example test/salt/pillar/debian.sls test/salt/pillar/redhat.sls test/salt/pillar/suse.sls
+        # Install and run `commitlint`
         - npm install @commitlint/config-conventional -D
         - npm install @commitlint/travis-cli -D
         - commitlint-travis
-    # Define the release stage that runs semantic-release
+    # Define the release stage that runs `semantic-release`
     - stage: release
       language: node_js
       node_js: lts/*

.yamllint

+# -*- coding: utf-8 -*-
+# vim: ft=yaml
+---
+# Extend the `default` configuration provided by `yamllint`
+extends: default
+
+# Files to ignore completely
+# 1. All YAML files under directory `node_modules/`, introduced during the Travis run
+ignore: |
+  node_modules/
+
+rules:
+  line-length:
+    # Increase from default of `80`
+    # Based on https://github.com/PyCQA/flake8-bugbear#opinionated-warnings (`B950`)
+    max: 88

pillar.example

+# -*- coding: utf-8 -*-
+# vim: ft=yaml
+---
 ## php.ng pillar examples
 
 php:
   # Use the following values to mute deprecation warnings
-  warning_messages:                                                          #
-    v1.0.0:                                                                  #
-      mute_critical: True                                                    #
-      mute_upcoming: True                                                    #
+  warning_messages:
+    v1.0.0:
+      mute_critical: true
+      mute_upcoming: true
   # Use external repository instead the default (only Ubuntu family)
-  use_external_repo: True
+  use_external_repo: true
   # Set the external repository name (valid only if use_external_repo is not none)
   external_repo_name: 'ondrej/php'
   # Use Software Collections Repository offering PHP 5.4, 5.5, 5.6, 7.0 and 7.1
   # https://www.softwarecollections.org/en/ for more information.
   # SCL is only supported on RHEL and CentOS and only active when using php.ng
-  use_scl_repo: True
+  use_scl_repo: true
   # Which PHP version from the SCL repos to use
   scl_php_version: 71
   # Set the MongoDB driver version. You can specify (optionally) the driver version
         # to pass forward special arguments to the pkg.installed call
         # you MUST include the name argument for this to work
         cli:
-           -
-             name: php-cli
-             fromrepo: my-specialrepo
-           -
-             name: php-common
-             skip_verify: True
+          -
+            name: php-cli
+            fromrepo: my-specialrepo
+          -
+            name: php-common
+            skip_verify: true
 
       # php-fpm os-specific settings
       fpm:
 
       # settings for the php-fpm service
       service:
-        # if True, enables the php-fpm service, if False disables it
-        enabled: True
+        # if true, enables the php-fpm service, if false disables it
+        enabled: true
         # additional arguments passed forward to
         # service.enabled/disabled
         opts:
-          reload: True
+          reload: true
 
       # settings for the relevant php-fpm configuration files
       config:
         ini:
           # arguments passed through to file.managed
           opts:
-            recurse: True
+            recurse: true
           # php.ini file contents that will be merged with the
           # defaults in php.ng.ini.defaults. See php.ng.ini.defaults for
           # syntax guidelines.
         conf:
           # arguments passed through to file.managed
           opts:
-            recurse: True
+            recurse: true
           # php-fpm conf file contents that will be merged with
           # php.ng.lookup.fpm.defaults. See php.ng.ini.defaults for
           # ini-style syntax guidelines.
 
       # settings for fpm-pools
       pools:
-        # defaults will apply for each pools settings and can be overwritten by pool settings
+        # defaults will apply for each pools settings and can be overwritten
+        # by pool settings
         defaults:
           user: nginx
           group: nginx
         # name of the pool file to be managed, this will be appended
         # to the path specified in php.ng.lookup.fpm.pools
         'mypool.conf':
-          # If true, the pool file will be managed, if False it will be
+          # If true, the pool file will be managed, if false it will be
           # absent
-          enabled: True
+          enabled: true
 
           # Overwrite the filename for ext_pillar that doesn't allow
           # dots in fields names.
 
           # arguments passed forward to file.managed or file.absent
           opts:
-             replace: False
+            replace: false
 
           # pool file contents. See php.ng.ini.defaults for ini-style
           # syntax guidelines.
       ini:
         # opts passed forward directly to file.managed
         opts:
-          replace: False
+          replace: false
         # contents of the php.ini file that are merged with defaults
         # from php.ng.ini.defaults. See php.ng.ini.defaults for ini-style
         # syntax guidelines
       # its contents will be joined by commas in final rendering.
       defaults:
         PHP:
-          engine: on
+          engine: 'On'
           output_buffering: 4096
           disable_functions:
             - pcntl_alarm
       - mysql
 
     # When using php.ng.apache2 on FreeBSD:
-    # Set this to False if you're not using apache-formula
-    use_apache_formula: True
+    # Set this to false if you're not using apache-formula
+    use_apache_formula: true

test/integration/default/inspec.yml

+# -*- coding: utf-8 -*-
+# vim: ft=yaml
+---
 name: default
 title: php formula
 maintainer: SaltStack Formulas