Remove Ruby version declaration in Gemfile
Remove Ruby version declaration in Gemfile

It prevents Travis from running different Ruby versions and it duplicates
the .ruby-version anyway.

ferdinandrosario/orientation,codio/orientation,splicers/orientation,orientation/orientation,orientation/orientation,IZEA/orientation,orientation/orientation,orientation/orientation,splicers/orientation,hashrocket/orientation,twinn/orientation,cmckni3/orientation,codeschool/orientation,cmckni3/orientation,LogicalBricks/orientation,IZEA/orientation,codeschool/orientation,friism/orientation,robomc/orientation,ferdinandrosario/orientation,splicers/orientation,codeschool/orientation,liufffan/orientation,Scripted/orientation,robomc/orientation,twinn/orientation,codio/orientation,liufffan/orientation,jefmathiot/orientation,friism/orientation,hashrocket/orientation,cmckni3/orientation,LogicalBricks/orientation,jefmathiot/orientation,Scripted/orientation,Scripted/orientation