Playground: Fails to run some code with Unicode.

[dmitshur]

Reporting for posterity.

Playground fails to run some code that contains Unicode. It doesn't always happen though.

The following fails:

https://gopherjs.github.io/playground/#/KEPVGsOG_W

However, the following works ok:

https://gopherjs.github.io/playground/#/KEPVGsOG_W

GopherJS itself executes both programs fine.