Somehow some (but not all) git helper scripts got the wrong interpreter. This
fixes them to use /usr/bin/env.

TBR=agable@chromium.org
BUG=

Review URL: https://codereview.chromium.org/212293002

git-svn-id: svn://svn.chromium.org/chrome/trunk/tools/depot_tools@259522 0039d316-1c4b-4281-b951-d872f2087c98