Add configs for JSON Schema files (`.json`)

* Ensure that files labeled with the `application/schema+json` media
  type are served compressed and are not cached.

* Since files containing JSON Schemas use the `.json` extension, they
  won't be served with any of the `HTML` document related headers and
  their specific character encoding will be `UTF-8`.

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Note: Because these types of files don't have their own specific file
extension and we can't know exactly if the `.json` file will contain a
JSON schema or just regular JSON, setting the media type (namely:
`application/schema+json`) will have to be done by the user, either by
configuring Apache (e.g.: https://github.com/h5bp/server-configs-apache/blob/58fb1d1b74cac4963d22ab018b77c80f595861fd/dist/.htaccess#L152-L174),
or from the level "beneath" the server (e.g.: from PHP).

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Thanks @fruitl00p!

Ref http://json-schema.org/latest/json-schema-core.html
    h5bp/server-configs-apache#39

Close h5bp/server-configs-apache#39