message: docs(timeinterval): update description for timeInterval
diff: @@ -15,6 +15,8 @@ import { map } from './map';
  * defaults to {@link asyncScheduler}, so by default, the `interval` will be in
  * milliseconds.
  *
  + * <span class="informal">Convert an Observable that emits items into one that
  + * emits indications of the amount of time elapsed between those emissions.</span>
  *
  * ![](timeinterval.png)
  *
  