Ignore FileName Rubocop cop

The `FileName` cop (available as of Rubocop 0.19.0) checks the filename
of the source files. Since `haml-lint` uses a temporary file its always
invalid. Add it to the ignore list.

Also sorted list of cops by name while we were here.

Change-Id: I73390d63e47a6fe4e67a2d2d2c290600e016e4c3
Reviewed-on: http://gerrit.causes.com/36243
Tested-by: jenkins <jenkins@causes.com>
Reviewed-by: Shane da Silva <shane@causes.com>