contrib/hooks/setgitperms.perl: use a lowercase "usage:" string

Make the usage string consistent with Git.

Reviewed-by: Jonathan Nieder <jrnieder@gmail.com>
Signed-off-by: David Aguilar <davvid@gmail.com>
Signed-off-by: Junio C Hamano <gitster@pobox.com>

contrib/hooks/setgitperms.perl

@@ -24,7 +24,7 @@
 use File::Basename;
 
 my $usage =
-"Usage: setgitperms.perl [OPTION]... <--read|--write>
+"usage: setgitperms.perl [OPTION]... <--read|--write>
 This program uses a file `.gitmeta` to store/restore permissions and uid/gid
 info for all files/dirs tracked by git in the repository.