commit: suggest --amend --reset-author to fix commiter identity

Since the message advises to fix the configuration first, the
advantage of using this command is that it is cut-and-paste ready,
while using --author='...' requires the user to type his name and
email again.

Signed-off-by: Matthieu Moy <Matthieu.Moy@imag.fr>
Acked-by: Jeff King <peff@peff.net>
Signed-off-by: Junio C Hamano <gitster@pobox.com>

builtin/commit.c

@@ -45,9 +45,9 @@ static const char implicit_ident_advice[] =
 "    git config --global user.name \"Your Name\"\n"
 "    git config --global user.email you@example.com\n"
 "\n"
-"If the identity used for this commit is wrong, you can fix it with:\n"
+"After doing this, you may fix the identity used for this commit with:\n"
 "\n"
-"    git commit --amend --author='Your Name <you@example.com>'\n";
+"    git commit --amend --reset-author\n";
 
 static const char empty_amend_advice[] =
 "You asked to amend the most recent commit, but doing so would make\n"