Use `const` and `let` over `var` about clean-code-javascript

[schoenwaldnils]

I even just started to edit for a PR, but then there were so much changes to make ^^

I highly recommend this screencast from laracast:
https://laracasts.com/series/es6-cliffsnotes/episodes/3

I personally don't use var anymore and default to const.
And if the value changes, I change it to let.

I could open a PR with my method, if the wish is there.

[ryanmcdermott]

@schoenwaldnils has an awesome fix so I'm going to close this issue once that is merged in with minor tweaks. Thanks CodinCat for your help!

[ryanmcdermott]

Thank you for sussing out the inconsistencies. We do need a coherent stance on this. @ericelliott has a good article about this, to use as inspiration so we could also elaborate more on the ES6 constants section.

[ryanmcdermott]

This was addressed in #51. Thanks for all of your help!