simplify encoding logic: no more chomping required

[pvdb]

As per #326 (comment)

I think https://ruby-doc.org/stdlib/libdoc/base64/rdoc/Base64.html#method-i-strict_encode64 would make this even more simple and not require calling #chomp

All done now... test still pass! 👍

[HarlemSquirrel]

Thank you!