Typo in the docs

[joostvanhoof]

Sorry not sure how to post improvements to the docs, I'm sure this finds its way.

On the x-on page there's a table with Modifiers and its corresponding Keyboard Key.

The modifiers for the arrow keys are incorrectly listed:

up should be arrow-up
down should be arrow-down
left should be arrow-left
right should be arrow-right

Just found this out while I was halfway through writing a bug report 😃

[joshhanley]

@joostvanhoof the docs are in this same repo under Packages>Docs, so just a PR to that is all thats required :)