git-svn: 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>

git-svn.perl

@@ -382,7 +382,7 @@ sub usage {
 	my $fd = $exit ? \*STDERR : \*STDOUT;
 	print $fd <<"";
 git-svn - bidirectional operations between a single Subversion tree and git
-Usage: git svn <command> [options] [arguments]\n
+usage: git svn <command> [options] [arguments]\n
 
 	print $fd "Available commands:\n" unless $cmd;