wikiheaders.pl: Add --copy-to-header option.

...because I keep mistyping it without the 's' on the end.  :/

build-scripts/wikiheaders.pl

@@ -12,6 +12,7 @@ my $copy_direction = 0;
 foreach (@ARGV) {
     $warn_about_missing = 1, next if $_ eq '--warn-about-missing';
     $copy_direction = 1, next if $_ eq '--copy-to-headers';
+    $copy_direction = 1, next if $_ eq '--copy-to-header';
     $copy_direction = -1, next if $_ eq '--copy-to-wiki';
     $srcpath = $_, next if not defined $srcpath;
     $wikipath = $_, next if not defined $wikipath;