add note about uninstalling old versions of grunt
add note about uninstalling old versions of grunt

paulcbetts/grunt,yonglehou/grunt,coldrye-collaboration/grunt,modulexcite/grunt,ThiagoGarciaAlves/grunt,thecc4re/gruntjs,yosiazwan/grunt,felixgrey/grunt,Chhunlong/grunt,paladox/grunt,abraheem/grunt,r14r/fork_grunt_master,vladikoff/grunt,arosa81/grunt,goodeggs/grunt,FeodorFitsner/grunt,lkiarest/grunt,eelve/grunt,zackexplosion/grunt,shama/grunt,thejameskyle/grunt,r14r-work/fork_grunt_master,yuhualingfeng/grunt,imjerrybao/grunt,JaKXz/grunt,fscherwi/grunt,IveWong/grunt,youmyyou/grunt,pandeysoni/grunt,q310550690/grunt