try crodwin
Replace ACRA with Fabric's Crashlytics.
Fully specifiy Fabric Plugin version
Remove superflous Crashlytics deps/definitions
add toast if api keys are missing, fixes #157
Fix ProGuard errors caused by stripped down GMS lib
Remove false signing config for release builds
Merge pull request #158 from gdg-x/feature/acra_to_fabric

Replace ACRA with Fabric's Crashlytics.
Update contribution guide to include git flow

As of yesterday we are using the git flow branching model in this project ( http://nvie.com/posts/a-successful-git-branching-model/ ). The default development branch for the next version is now `develop`, `master` only carries the status of released version (basically a history of all tags).

To use git flow you can use normal git commands or apply a number of plugins for [command line](https://github.com/nvie/gitflow), [Android Studio/IntelliJ](https://plugins.jetbrains.com/plugin/3033?pr=idea) or [SourceTree (built-in)](http://www.sourcetreeapp.com/).
Update SDK to 24.0.2, extract version numbers into variables for easier maintanance
Build only master and develop
Merge pull request #160 from gdg-x/feature/travis_update

Update SDK to 24.0.2, extract version numbers into variables for easier maintanance
Merge branch 'develop' into feature/update_readme