[javascript mode] Support s regexp flag

Issue #5396

Author: marijnh

mode/javascript/javascript.js

@@ -96,7 +96,7 @@ CodeMirror.defineMode("javascript", function(config, parserConfig) {
         return ret("comment", "comment");
       } else if (expressionAllowed(stream, state, 1)) {
         readRegexp(stream);
-        stream.match(/^\b(([gimyu])(?![gimyu]*\2))+\b/);
+        stream.match(/^\b(([gimyus])(?![gimyus]*\2))+\b/);
         return ret("regexp", "string-2");
       } else {
         stream.eat("=");