JavaScript/ES6 solution has formatting problems and non-working example for chapter two

[Alexandr Shulaev]

1. All solutions for JS for the second chapter have a problem: it changes the source array by reference. Expected behavior: a function call creates a new sorted array without changing the source;
2. For formatting JavaScript code is better to use Prettier. This will help in all examples to make the same formatting and it will look better.

[Alexandr Shulaev]

I fixed it here #129