message: Flag componentWillUpdate as UNSAFE in MatrixChat
  For
diff: @@ -360,7 +360,8 @@ export default createReactClass({
  if (this._accountPasswordTimer !== null) clearTimeout(this._accountPasswordTimer);
  },
  - componentWillUpdate: function(props, state) {
  + // TODO: [REACT-WARNING] Replace with appropriate lifecycle stage
  + UNSAFE_componentWillUpdate: function(props, state) {
  if (this.shouldTrackPageChange(this.state, state)) {
  this.startPageChangeTimer();
  }
  @@ -381,7 +382,7 @@ export default createReactClass({
  // Tor doesn't support performance
  if (!performance || !performance.mark) return null;
  - // This shouldn't happen because componentWillUpdate and componentDidUpdate
  + // This shouldn't happen because UNSAFE_componentWillUpdate and componentDidUpdate
  // are used.
  if (this._pageChanging) {
  console.warn('MatrixChat.startPageChangeTimer: timer already started');
  