Adding mongodb service to travis.
Update mongoid_magic_counter_cache.gemspec

Adding license to gemspec.
Fixing .travis.yml merge conflict.
Merge pull request #13 from jah2488/Sameer-Tilak-master

Condition added for counter cache
Refactoring out a lot of uneeded duplication.
Removing version flag.
Version bump.
Update .travis.yml
Updated READ.me with conditional counter example.