git svn: consistent spacing after "W:" in warnings

All other instances of "W:"-prefixed warning messages have a space after
the "W:" to help with readability.

Signed-off-by: Eric Wong <normalperson@yhbt.net>

perl/Git/SVN.pm

@@ -1504,7 +1504,7 @@ sub lookup_svn_merge {
 		my $top_commit = $gs->find_rev_before( $top, 1, $bottom );
 
 		unless ($top_commit and $bottom_commit) {
-			warn "W:unknown path/rev in svn:mergeinfo "
+			warn "W: unknown path/rev in svn:mergeinfo "
 				."dirprop: $source:$range\n";
 			next;
 		}