Fix `AddOutputFilterByType` related error

* For some odd reason having:

    AddOutputFilterByType DEFLATE ...
                                  application/vnd.geo+json \
                                  ...
                                  application/x-web-app-manifest+json \
                                  ...

  causes an internal server error in Apache 2.4.x.

* This commit fixes the issue by surrounding the media types
  with quotes:

    AddOutputFilterByType DEFLATE ...
                                  "application/vnd.geo+json" \
                                  ...
                                  "application/x-web-app-manifest+json" \
                                  ...