[skip ci] Update README: Rails 4.2.1 and 5.0.0
[skip ci] Update README: Rails 4.2.1 and 5.0.0

guilleva/ransack,johan--/ransack,laserlemon/ransack,martndemus/ransack,outstand/ransack,roman-franko/ransack,activerecord-hackery/ransack,Eric-Guo/ransack,AndrewSwerlick/ransack,reinteractive/ransack,mariorcardoso/ransack,Mario245/ransack,avit/ransack