pre-push.sample: Write error message to stderr
pre-push.sample: Write error message to stderr

githooks(5) suggests:

  Information about why the push is rejected may be sent to the user
  by writing to standard error.

So follow that advice in the sample.

Signed-off-by: W. Trevor King <f75897670c17327c42ab201733fb8a81ff9f4c34@tremily.us>
Signed-off-by: Junio C Hamano <a6723cc3f76163bf7adb636a73ac3b0ceb3e6b9b@pobox.com>

destenson/git,destenson/git,destenson/git,destenson/git,destenson/git,destenson/git,destenson/git,destenson/git