Update Gemfile to use https

Resolves following warning when bundling:

  > The source :rubygems is deprecated because HTTP requests are insecure.
  > Please change your source to 'https://rubygems.org' if possible, or 'http://rubygems.org' if not. 
Merge pull request #51 from bjeanes/patch-1

Update Gemfile to use https
Add a database-backed LRU cache of git-blame results
Update Gemfile.lock
Fix index
* Lazy-create Deploys if build and revision are given to notify
* Refactor OccurrencesWorker
Don't assume that public path is #{root}/public

Reflecting on the configured public directory allows custom 404 serving even when the public directory is moved (e.g. in .war files generated by warbler).
Merge pull request #55 from bjeanes/patch-2

Don't assume that public path is #{root}/public