docs(readme): fix `rstcheck` violation [skip ci]

https://travis-ci.org/github/myii/apache-formula/builds/731605038#L255

```
docs/README.rst:151: (ERROR/3) Unknown target name: "apache mod_security2 waf`<http://modsecurity.org/>".
```

docs/README.rst

@@ -159,7 +159,7 @@ Installs and enables the mod_dav_svn module (Debian only)
 ``apache.config.modules.mod_security``
 ^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^
 
-Installs an enables the `Apache mod_security2 WAF`<http://modsecurity.org/>`_
+Installs an enables the `Apache mod_security2 WAF <http://modsecurity.org/>`_
 using data from Pillar. (Debian and RedHat Only)
 
 Allows you to install the basic Core Rules (CRS) and some basic configuration for mod_security2