Some specs fail on 3.1.0-stable because of updated dependencies. This PR updates specs to pass, mirroring changes on master. Hope this helps! :koala:

1. i18n v0.7.0 enforce_available_locales now defaults to true:
fix mirrors PR to master (https://github.com/mongoid/mongoid/pull/3899)

2. Changing behavior in MongoDB 2.6+:
fix mirrors commit to master (https://github.com/mongoid/mongoid/commit/e93a4837b0266db46c24aae172e184f57c847b04)

3. Moped::Errors::QueryFailure message change:
fix mirrors commit to master (https://github.com/mongoid/mongoid/commit/fa57fca58a19b7eba4ac03cdaacee57a8924145e)