playground: Use https to access snippet store.

[dmitshur]

Snippet store now supports https. Loading resources over https is always okay, even on pages served via http (the other way around is a problem).

References:

• https://developer.mozilla.org/en-US/docs/Web/Security/Mixed_content
• https://developers.google.com/web/fundamentals/security/prevent-mixed-content/what-is-mixed-content
• https://stackoverflow.com/q/20516584

Helps #37.

[dmitshur]

Ok, everything looks good.

Before:

After:

I'll change http://snippets.gopherjs.org to redirect to https:// instead of serving directly.

[dmitshur]

I'll change http://snippets.gopherjs.org to redirect to https:// instead of serving directly.

Done. 🎉