message: cancel the edit when pressing escape
diff: @@ -107,10 +107,12 @@ export default class MessageEditor extends React.Component {
  } else if (event.key === "Enter") {
  this._sendEdit();
  event.preventDefault();
  + } else if (event.key === "Escape") {
  + this._cancelEdit();
  }
  }
  - _onCancelClicked = () => {
  + _cancelEdit = () => {
  dis.dispatch({action: "edit_event", event: null});
  }
  @@ -185,7 +187,7 @@ export default class MessageEditor extends React.Component {
  ref={ref => this._editorRef = ref}
  ></div>
  <div className="mx_MessageEditor_buttons">
  - <AccessibleButton kind="secondary" onClick={this._onCancelClicked}>{_t("Cancel")}</AccessibleButton>
  + <AccessibleButton kind="secondary" onClick={this._cancelEdit}>{_t("Cancel")}</AccessibleButton>
  <AccessibleButton kind="primary" onClick={this._sendEdit}>{_t("Save")}</AccessibleButton>
  </div>
  </div>;
  