use correct option in favicon_mongler

bin/favicon_mongler.pl

@@ -20,7 +20,7 @@ my %files = (
 );
 foreach my $size ( sort { $b <=> $a } keys(%files) ) {
     print "*** Generating ${size}x${size} .$files{$size} now... ***\n";
-    my @cmd = ( $bin, '-w', $size, '-h', $size, $icon, '-e', "$dir/favicon-$size.$files{$size}" );
+    my @cmd = ( $bin, '-w', $size, '-h', $size, $icon, '-o', "$dir/favicon-$size.$files{$size}" );
     system(@cmd) && die "Failed to run @cmd: $!";
     print "*** Wrote $dir/favicon-$size.$files{$size} ***\n\n";
 }