message: Persist contentState when sending SlashCommand via MessageComposerInput
diff: @@ -723,6 +723,7 @@ export default class MessageComposerInput extends React.Component {
  const cmd = SlashCommands.processInput(this.props.room.roomId, commandText);
  if (cmd) {
  if (!cmd.error) {
  + this.historyManager.save(contentState, this.state.isRichtextEnabled ? 'html' : 'markdown');
  this.setState({
  editorState: this.createEditorState(),
  });
  