fix(init): replace `gid_from_name` (deprecated in `develop`)

* Close #198
* All details in that issue
* Solution based upon:
  - https://github.com/saltstack-formulas/vault-formula/pull/35#issuecomment-509854411

users/init.sls

@@ -144,7 +144,7 @@ users_{{ name }}_user:
     {% elif 'prime_group' in user and 'name' in user['prime_group'] %}
     - gid: {{ user['prime_group']['name'] }}
     {% else -%}
-    - gid_from_name: True
+    - gid: {{ name }}
     {% endif -%}
     {% if 'fullname' in user %}
     - fullname: {{ user['fullname'] }}