Allow repository names to contain dots.

Before this commit repository names which contain dots point
to wrong repositories.

Examples:
* http://travis-lite.com/henrikhodne/davinci.rb -> henrikhodne/davinci
* http://travis-lite.com/kytrinyx/exercism.io -> kytrinyx/exercism

Note that had to extract the show route as a member to make the regexp work.
It didn't work on `resources :repositories`.