message: Scroll to the bottom of editor if on last line
  Make the MessageComposerInput scroll to the bottom if we are on the last line of the contents.
  fixes
diff: @@ -451,14 +451,20 @@ export default class MessageComposerInput extends React.Component {
  callback();
  }
  - if (this.props.onContentChanged) {
  - const textContent = this.state.editorState
  - .getCurrentContent().getPlainText();
  + const textContent = this.state.editorState.getCurrentContent().getPlainText();
  const selection = RichText.selectionStateToTextOffsets(
  this.state.editorState.getSelection(),
  this.state.editorState.getCurrentContent().getBlocksAsArray());
  + if (this.props.onContentChanged) {
  this.props.onContentChanged(textContent, selection);
  }
  +
  + // Scroll to the bottom of the editor if the cursor is on the last line of the
  + // composer. For some reason the editor won't scroll automatically if we paste
  + // blocks of text in or insert newlines.
  + if (textContent.slice(selection.start).indexOf("\n") === -1) {
  + this.refs.editor.refs.editor.scrollTop = this.refs.editor.refs.editor.scrollHeight;
  + }
  });
  }
  