Revert composer.json to use 2.1 versions again instead of `dev-master`.
Revert composer.json to use 2.1 versions again instead of `dev-master`.

fabpot/Silex,GromNaN/Silex,GromNaN/Silex,mTorres/Silex,mathroc/Silex,jdreesen/Silex,lyrixx/Silex,fhinkel/Silex,mmauri04/Silex,romainneutron/Silex,Seldaek/Silex,RayRutjes/Silex,cgsmith/Silex,arduanov/Silex,tcx1000/Silex,romainneutron/Silex,lokhman/Silex,naderman/Silex,peterkokot/Silex,plotek/Silex,SpacePossum/Silex,RayRutjes/Silex,plotek/Silex,stof/Silex,Incognito/silex-fork,tcx1000/Silex,CarsonF/Silex,stof/Silex,naderman/Silex,CarsonF/Silex,Xephi/Silex,Tobion/Silex,peterkokot/Silex,beealone/Silex,cgsmith/Silex,mmauri04/Silex,Tobion/Silex,gencer/Silex,romainneutron/Silex,cesarmarinhorj/Silex,akucherevskiy/developex_test,jdreesen/Silex,CarsonF/Silex,stof/Silex,lyrixx/Silex,lokhman/Silex,fabpot/Silex,mTorres/Silex,naderman/Silex,SanderKnape/Silex,Tobion/Silex,peterkokot/Silex,akucherevskiy/developex_test,SanderKnape/Silex,cesarmarinhorj/Silex,beealone/Silex,Incognito/silex-fork,silexphp/Silex,SpacePossum/Silex,arduanov/Silex,JPry/Silex,JPry/Silex,Xephi/Silex,mathroc/Silex,Seldaek/Silex,fhinkel/Silex,akucherevskiy/developex_test,GromNaN/Silex,lyrixx/Silex