JavaScript/ES6 solution has formatting problems for chapter nine

[Alexandr Shulaev]

1. 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.
2. Example in folder grokking_algorithms/09_dynamic_programming/ES6/examples/ describes the same example as grokking_algorithms/09_dynamic_programming/ES6/01_longest_common_subsequence.js
   I think need to remove duplication and leave only a working example. Non-working input diff('fosh', 'fish') // displays 2, but correct 3

[Alexandr Shulaev]

I fixed it here #143