commit: quote the user name in the example

If the user runs

 git config --global user.name Your Name

as suggested, user.name will be set to "Your".  With this patch, the
suggested command will be

 git config --global user.name "Your Name"

which will set user.name to "Your Name" and hopefully help users avoid
the former mistake.
Signed-off-by: NMatt Kraai <kraai@ftbfs.org>
Signed-off-by: NJunio C Hamano <gitster@pobox.com>

builtin-commit.c

@@ -41,7 +41,7 @@ static const char implicit_ident_advice[] =
 "on your username and hostname. Please check that they are accurate.\n"
 "You can suppress this message by setting them explicitly:\n"
 "\n"
-"    git config --global user.name Your Name\n"
+"    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"