Update to zen-observable v0.3.0 which implements several changes to the
spec, the most notable of which is that Observable.{of, from, forEach}
are now all synchronous [1].

To preserve the previous behavior of `selections()` where no events were
emitted until the next tick of the event loop, add a delay before
checking for the initial selection.

[1] https://github.com/zenparsing/es-observable/issues/88