Documentation/git-push: --all, --mirror, --tags can not be combined

While b259f09 made git-push output a better error message for 'git-push
--all --tags', this commit fixes the synopsis in the documentation.

Inconsistency spotted and fix suggested by Jari Aalto through
 http://bugs.debian.org/502567

Signed-off-by: Gerrit Pape <pape@smarden.org>
Signed-off-by: Junio C Hamano <gitster@pobox.com>

Documentation/git-push.txt

@@ -9,7 +9,7 @@ git-push - Update remote refs along with associated objects
 SYNOPSIS
 --------
 [verse]
-'git push' [--all | --mirror] [--dry-run] [--tags] [--receive-pack=<git-receive-pack>]
+'git push' [--all | --mirror | --tags] [--dry-run] [--receive-pack=<git-receive-pack>]
 	   [--repo=<repository>] [-f | --force] [-v | --verbose]
 	   [<repository> <refspec>...]