fix(ConnectionMock.spec.js): test `beforeTask` rather than `onZoneEnter`

https://github.com/angular/prophecy/commit/aa82cc801524e671fd9efff418ad4714ba30b39f has changed to
use new zone.js api, causing this test to fail. An update is needed here as well.

Closes #25
feat(jsonp): implement basic JSONP transport