Since Ruby 2.0.0 is stable now, I've removed it from the allowed
failures in Travis. It's only allowed to fail with Sinatra edge as 1.9.3
does.

It is also tested in the same way that 1.9.3 is (see matrix includes) - feel free to remove
this if it adds too much overhead to the testing process in Travis.

As a final note, I've added myself and Igor to the notifications'
recipients list.
Merge pull request #1079 from padrino/update-travis-on-ruby-2.0.0

Update Travis on Ruby 2.0.0