Fixed grunt master to work with submodules correctly (#10566)
Fixed grunt master to work with submodules correctly (#10566)

refs #9441

`grunt master` should only error if there are changes to tracked files which have not been committed - this ensures no work is lost.
JohnONolan/Ghost,JohnONolan/Ghost,Gargol/Ghost,kevinansfield/Ghost,bitjson/Ghost,Kikobeats/Ghost,Kikobeats/Ghost,e10/Ghost,e10/Ghost,ErisDS/Ghost,ErisDS/Ghost,kevinansfield/Ghost,TryGhost/Ghost,TryGhost/Ghost,bitjson/Ghost,kevinansfield/Ghost,Gargol/Ghost,janvt/Ghost,JohnONolan/Ghost,Kikobeats/Ghost,ErisDS/Ghost,janvt/Ghost,TryGhost/Ghost