Minor fixes to JavaScript and README

[gazayas]

Besides the changes I added here, the following two methods stood out to me:

1. keyDownFunction
2. keyUpFunction

There's some duplicate code here so I'd be glad to refactor some of it, but it looks like these methods aren't being used in the first place:

https://github.com/bullet-train-co/magic_test/blob/b086d2f9bdfcbbe1b3d5283fa10fd5877f73256b/app/views/magic_test/_listeners.html#L2-L3

For that reason I won't worry about it too much now, but if we just want to get rid of these methods I can go head and delete them.