Make pkg argument optional for lerna diff (#831)
Make pkg argument optional for lerna diff (#831)

This also hides the progress bar, which is not needed for diff.

Fixes #816
evocateur/lerna,evocateur/lerna,tbayaa/lerna,sebmck/lerna,treshugart/lerna,lerna/lerna,kittens/lerna,lerna/lerna,FaHeymann/lerna,lerna/lerna