not working with ES6

[kaeferfreund]

Hi Maga,

thanks for you great work! Unfortunately in some envs it is not possible to control the ES Version, so in my case i needed to comply with ES6. I have forked and adapted your lib (https://github.com/kaeferfreund/oid64) to work with ES6.

Maybe there is a way to incorporate my changes upstream to a version that is compatible with different ES versions?