git-stash.txt: remove extra square bracket

In 1ada5020b3 ("stash: use stash_push for no verb form", 2017-02-28), when the pathspec argument was introduced in 'git stash', that was also documented. However I forgot to remove an extra square bracket after the '--message' argument, even though the square bracket should have been after the pathspec argument (where it was also added).

Remove the extra square bracket after the '--message' argument, to show that the pathspec argument should be used with the 'push' verb.

While the pathspec argument can be used without the push verb, that's a special case described later in the man page, and removing the first extra square bracket instead of the second one makes the synopis easier to understand.

---
 Documentation/git-stash.txt | 2 +-
 1 file changed, 1 insertion(+), 1 deletion(-)

index 056dfb8661..7ef8c47911 100644
@@ -14,7 +14,7 @@ SYNOPSIS
 'git stash' ( pop | apply ) [--index] [-q|--quiet] [<stash>]
 'git stash' branch <branchname> [<stash>]
 'git stash' [push [-p|--patch] [-k|--[no-]keep-index] [-q|--quiet]
-	     [-u|--include-untracked] [-a|--all] [-m|--message <message>]]
+	     [-u|--include-untracked] [-a|--all] [-m|--message <message>]
 	     [--] [<pathspec>...]]
 'git stash' clear
 'git stash' create [<message>]

2.17.0.rc1.35.g90bbd502d5.dirty