fix aggregation GroupField
Fixes #109, #107: authenticate on MongoDBSystem actor startup
Merge pull request #113 from ornicar/fixGroupField

fix aggregation GroupField
Merge branch 'master' of https://github.com/zenexity/ReactiveMongo into afresh-play22-iliaz

* 'master' of https://github.com/zenexity/ReactiveMongo:
  Fixes #109, #107: authenticate on MongoDBSystem actor startup
  fix aggregation GroupField
v 1.0.7 with play 2.2.0