[javascript mode] Add test for bigint literals

Author: tmcw

mode/javascript/test.js

@@ -268,6 +268,8 @@
      "[keyword const] [def async] [operator =] {[property a]: [number 1]};",
      "[keyword const] [def foo] [operator =] [string-2 `bar ${][variable async].[property a][string-2 }`];")
 
+  MT("bigint", "[number 1n] [operator +] [number 0x1afn] [operator +] [number 0o064n] [operator +] [number 0b100n];")
+
   MT("async_comment",
      "[keyword async] [comment /**/] [keyword function] [def foo]([def args]) { [keyword return] [atom true]; }");