[INTERNAL] grunt task lastchange: do not fail if git command fails

Change-Id: I36a96047cdd793b41aaef3369d1506d5dcc948e4
(cherry picked from commit 414ac1b024e722723db3e30c1c59a8649dc2e7ec)
CR-Id: 012006153200015038712014
Merge "[INTERNAL] grunt task lastchange: do not fail if git command fails" into rel-1.26