fix 'uninitialized constant Gabba::Gabba::VERSION' exception

Otherwise I get something like this 

```lib/gabba/gabba.rb:17:in `<class:Gabba>': uninitialized constant Gabba::Gabba::VERSION (NameError)```

ENV:
ruby 2.0.0p247 (2013-06-27 revision 41674) [x86_64-darwin12.3.0]
rails 4.0