i18n: fix command template placeholder format

Signed-off-by: Jean-Noël Avila <jn.avila@free.fr>
Signed-off-by: Junio C Hamano <gitster@pobox.com>

Documentation/git-revert.txt

@@ -8,7 +8,7 @@ git-revert - Revert some existing commits
 SYNOPSIS
 --------
 [verse]
-'git revert' [--[no-]edit] [-n] [-m parent-number] [-s] [-S[<keyid>]] <commit>...
+'git revert' [--[no-]edit] [-n] [-m <parent-number>] [-s] [-S[<keyid>]] <commit>...
 'git revert' (--continue | --skip | --abort | --quit)
 
 DESCRIPTION

builtin/revert.c

@@ -21,7 +21,7 @@
  */
 
 static const char * const revert_usage[] = {
-	N_("git revert [--[no-]edit] [-n] [-m parent-number] [-s] [-S[<keyid>]] <commit>..."),
+	N_("git revert [--[no-]edit] [-n] [-m <parent-number>] [-s] [-S[<keyid>]] <commit>..."),
 	N_("git revert (--continue | --skip | --abort | --quit)"),
 	NULL
 };