Corrupted base64 encoding

[Jeff Simpson]

The padding for base64 encoding is adding one too many equal signs when the byte remainder is 1.

WebAssemblyStudio/src/util.ts

Line 135 in fbf7d4e

 base64 += concat3(encodings[a], encodings[b], "==="); 

This is based on a gist that correctly appends 2 equal signs:

https://gist.github.com/jonleighton/958841#file-base64arraybuffer-js-L53

[Yury Delendik]

Closed by #401