Update README concerning Rails 4.1.
Update README concerning Rails 4.1.

roman-franko/ransack,avit/ransack,AndrewSwerlick/ransack,guilleva/ransack,Eric-Guo/ransack,reinteractive/ransack,Mario245/ransack,martndemus/ransack,vaski/ransack,amboxer21/ransack,laserlemon/ransack,mariorcardoso/ransack,activerecord-hackery/ransack,nagyt234/ransack,praktijkindex/ransack,outstand/ransack,johan--/ransack