fix: escape braces in regex

Author: amaanq

grammar.js

@@ -1476,7 +1476,7 @@ module.exports = grammar({
         seq('\\', choice(
           /[^xu]/,
           /u[0-9a-fA-F]{4}/,
-          /u{[0-9a-fA-F]+}/,
+          /u\{[0-9a-fA-F]+\}/,
           /x[0-9a-fA-F]{2}/,
         )),
         /[^\\']/,
@@ -1489,7 +1489,7 @@ module.exports = grammar({
         choice(
           /[^xu]/,
           /u[0-9a-fA-F]{4}/,
-          /u{[0-9a-fA-F]+}/,
+          /u\{[0-9a-fA-F]+\}/,
           /x[0-9a-fA-F]{2}/,
         ),
       )),