git-remote-mediawiki: change the behaviour of a split

A "split ' '" is turned into a "split / /", which changes its behaviour: the
old method matched a run of whitespaces (/\s*/), while the new one will match a
single space, which is what we want here. Indeed, in other contexts,
changing split(' ') to split(/ /) could potentially be a regression, however,
here, when parsing the output of "rev-list --parents", whose output SHA-1's are
each separated by a single space, splitting on a single space is perfectly
correct.

Signed-off-by: Célestin Matte <celestin.matte@ensimag.fr>
Signed-off-by: Matthieu Moy <matthieu.moy@grenoble-inp.fr>
Signed-off-by: Junio C Hamano <gitster@pobox.com>

contrib/mw-to-git/git-remote-mediawiki.perl

@@ -1168,7 +1168,7 @@ sub mw_push_revision {
 		my %local_ancestry;
 		foreach my $line (@local_ancestry) {
 			if (my ($child, $parents) = $line =~ /^-?([a-f0-9]+) ([a-f0-9 ]+)/) {
-				foreach my $parent (split(' ', $parents)) {
+				foreach my $parent (split(/ /, $parents)) {
 					$local_ancestry{$parent} = $child;
 				}
 			} elsif (!$line =~ /^([a-f0-9]+)/) {