Fix error message in Safari - Semantic token play

See https://github.com/microsoft/monaco-editor/issues/2459 for details

website/playground/new-samples/extending-language-services/semantic-tokens-provider-example/sample.js

@@ -35,7 +35,7 @@ function getModifier(modifiers) {
     }
 }
 
-const tokenPattern = new RegExp('(?<=\\[)([a-zA-Z]+)((?:\\.[a-zA-Z]+)*)(?=\\])', 'g');
+const tokenPattern = new RegExp('([a-zA-Z]+)((?:\\.[a-zA-Z]+)*)', 'g');
 
 monaco.languages.registerDocumentSemanticTokensProvider('plaintext', {
     getLegend: function () {