use crypto.getRandomValues() for scramble extension

[lsching17]

crypto.getRandomValues() is more secure than Math.random() for scrambling keyboard

[Mottie]

Hi @lsching17!

Thanks for your work, but would you please add a check for window.crypto and fallback to using Math.random...

I noticed that IE11 & IE mobile require a ms prefix (msCrypto.getRandomValues()). And I know this library has been used on a raspberry pi and some tv's, so I don't really know if they support the crypto API.

[lsching17]

modified, now fall back in the following order: window.crypto -> window.msCrypto -> Math.Random

tested in IE11, Firefox 60 and Chromium 66

[Mottie]

Awesome, thanks!