perl/Git.pm: typofix in a comment

No change of behaviour intended.

Signed-off-by: Junio C Hamano <gitster@pobox.com>
diff --git a/perl/Git.pm b/perl/Git.pm
index 864123f..dd72d63 100644
--- a/perl/Git.pm
+++ b/perl/Git.pm
@@ -531,7 +531,7 @@
 =cut
 
 sub get_tz_offset {
-	# some systmes don't handle or mishandle %z, so be creative.
+	# some systems don't handle or mishandle %z, so be creative.
 	my $t = shift || time;
 	my $gm = timegm(localtime($t));
 	my $sign = qw( + + - )[ $gm <=> $t ];