add empty slice test for GroupBy
Merge pull request #6: GroupBy
update README.md with new feature
Removed extra ']' from Query.{Sum,Average} docs
Merge pull request #7 from elimisteve/master

Removed extra ']' from Query.{Sum,Average} docs
godoc fix for DistinctBy (fixes #10)
Update .travis.yml

missing dependency
Merge pull request #10 from dericofilho/master

Update .travis.yml with missing dependency