update_repo must use os.chdir().  calling os.system(cd

You probably want this change if you want update to work on linux.  Without this change, I see alot of:


fatal: Not a git repository (or any parent up to mount parent )
Stopping at filesystem boundary (GIT_DISCOVERY_ACROSS_FILESYSTEM not set).

This is because my cwd is not a git repo, and the system(cd <next git repo>) doesn't persist.