Better Regex

This is done to match the regex found here: https://github.com/MohammadYounes/rtlcss/blob/master/lib/directive-parser.js#L4

packages/scripts/config/webpack.config.js

@@ -84,7 +84,7 @@ const cssLoaders = [
 											{
 												discardComments: {
 													remove(comment) {
-														return !/(\!rtl)/.test(comment);
+														return !/^\s*!?\s*rtl:/.test(comment);
 													},
 												},
 												cssDeclarationSorter: false