Base64 decode fix

[haouarihk]

FIxed the issue with decode #786

Explained

I just corrected a little mistake @hikarunoryoma have made with
Buffer.from he did buffer.from(base64).toString("base64") which essentially takes in the base64 as a utf-8 and tries to convert it into a string of type "base64"

but instead it should be
buffer.from(base64, "base64") which is telling the buffer object to take that base64 and tell it it's a type of base64

[marco-c]

There are some test failures, strangely they were not present in your earlier PR. Maybe you changed something?

[marco-c]

Thanks!