Merge branch 'release/2.12.0' into develop

* release/2.12.0:
  fixed readme fixed minitest dependency
Merge branch 'hotfix/2.12.1' into develop

* hotfix/2.12.1:
  * Tested against Ruby 2.1.3
Improved readme
[ci skip]
* Tested against Rails 3.2.20, 4.0.11 and 4.1.7
* Open-ended dependencies for development gems
Merge branch 'release/2.13.0'

* release/2.13.0:
  * Tested against Rails 3.2.20, 4.0.11 and 4.1.7 * Open-ended dependencies for development gems
  Improved readme [ci skip]