fix atob() in Node.js. related dankogai#84
fix atob() in Node.js. related dankogai#84

problem:
    in Node.js,
    when atob() convert a base64 data with '=',
    unnecessary null bytes are added to the end of restored data.

dankogai/js-base64,dankogai/js-base64,dankogai/js-base64