Inaccuracy in introduction to ES6 challenges

The most recent standardized version is called ECMAScript 6 (ES6), released in 2015.

This should be amended. As far as I can tell, most of the cool new features of ECMAScript that people use come from ES6 but we have since had ES7, ES8 and ES9 / ES2018. Here is the latter:

www(dot)ecma-international(dot)org/ecma-262/9.0/index.html (←needed to evade the spam filter)

Perhaps the ES6 challenges should also eventually be extended to encompass features from the newer standards.