Bug: Randomness is not cryptographically secure

[markstos]

This module uses Math.random() is not really random.

A crypto secure solution would use crypto.getRandomBytes().

To fix this, the "create" function could use crypto-random-string

[markstos]

As an alternate solution to address this, I submitted a PR to crypto-random-string to add this character set as an option to that module: sindresorhus/crypto-random-string#14