Pin jsbin version number so that it shows the correct thing

The embedded jsbin was not pinned to a version, so it wasn't actually pointing at a jsbin that used both `registerHelper` and `registerAsyncHelper`.

This changes it to point at a pinned version of the jsbin (and I edited the jsbin to use both helpers, as the guide's text states).

Also, fwiw, I am able to edit the jsbin in question there. Perhaps it was mine originally, but again, since it is not pinned, that means I can edit it and make the embedded version on the ember guides say anything I want, which seems bad.