message: Patch delta manager.
diff: @@ -516,7 +516,8 @@ export class DeltaManager extends EventEmitter implements IDeltaManager<ISequenc
  assert.equal(message.sequenceNumber, this.baseSequenceNumber + 1);
  const startTime = Date.now();
  - if (message.contents && typeof message.contents === "string") {
  + // Remove after SPO picks up the latest build.
  + if (message.contents && typeof message.contents === "string" && message.type !== MessageType.ClientLeave) {
  message.contents = JSON.parse(message.contents);
  }
  