Fix WebGL test beds for JS and Wasm

[huy-nguyen]

Both WebGL test beds on the master branch do not work (Mac OS 10.15.5, Chrome 83) so I tried to fix them:

• Recompile both 2.2.1 and 2.3.1 with emcc version 1.39.16.
• Fix script file paths in both test beds to make scripts load correctly.