[javascript/en] var -> let/const

In the javascript tutorial the `var` keyword is introduced and used extensively, while `let` and `const` are only mentioned briefly under the ES6 additions section at the end. In this day and age, where ES6 is support is extremely common and use of `var` is essentially entirely been supplanted by `let` and `const`, wouldn't it make more sense to have `var` be the footnote instead?

I can make this change, I just want to see what ppl think