re-added Gruntfile to Makefile linting
re-added Gruntfile to Makefile linting

DoNotUseThisCodeJUSTFORKS/cryptocat,arno01/cryptocat,DGO143/cryptocat,wakermahmud/cryptocat,Raynes/cryptocat,DoNotUseThisCodeJUSTFORKS/cryptocat,DoNotUseThisCodeJUSTFORKS/cryptocat,PeterDaveHello/cryptocat,Cryptodog/cryptocat,DGO143/cryptocat,wakermahmud/cryptocat,PeterDaveHello/cryptocat,arno01/cryptocat,Raynes/cryptocat,DGO143/cryptocat,Cryptodog/cryptocat,Raynes/cryptocat