Upgrade sinatra to 1.4.2

Changes needed to upgrade to sinatra 1.4.2

- Use Rack:File instead of Sinatra::Base::StaticFile
- Redirects uses 303 http code for other verbs than GET
Merge pull request #109 from cloudfoundry/upgrade_sinatra

Upgrade sinatra to 1.4.2 [Fixes #46496455]