message: docs(MIGRATION.md): Add sample/sampleTime operator split
  When using a number interval, we must now use `sampleTime` instead of `sample`. This was not specified in the document.
diff: @@ -243,6 +243,15 @@ To reduce polymorphism and get better performance out of operators, some operato
  <td><code>timeout(dueTime: number | Date, other?: Observable | Promise, scheduler?: Scheduler)</code></td>
  <td><code>timeoutWith(due: number | Date, withObservable: ObservableInput, scheduler: Scheduler)</code></td>
  </tr>
  + <tr>
  + <td rowspan="2"><code>sample</code></td>
  + <td><code>sample(interval: number, scheduler?: Scheduler)</code></td>
  + <td><code>sampleTime(interval: number, scheduler?: Scheduler)</code></td>
  + </tr>
  + <tr>
  + <td><code>sample(notifier: Observable)</code></td>
  + <td><code>sample(notifier: Observable)</code></td>
  + </tr>
  </tbody>
  </table>
  