Support config file used in Fastlane

[erawhctim]

Fastlane uses a custom config file written in Ruby called a Fastfile, would it be possible to support these files just by modifying the Ruby section of config.coffee to include the file explicitly? e.g type: ["*.rb", "Fastfile"]

Happy to send a PR your way for the fix, but I just wasn't sure if there would be more work involved than just this one line change.

[r-chris]

I think this is coming to a point where we should provide a config for users to allow them to add their own file extensions for each language instead of hard-coding a fixed number of commonly used once into the source.