message: Work around draft-js-export-html#62 by post-processing <br>\n
  Fixes by post-processing the output HTML from draft-js-export-html by replacing `<br>\n` with `<br>`. This works for content within or outside of `<pre>`. If we replace with `\n` instead, the newlines only apply in `<pre>` tags so we use `<br>`.
diff: @@ -509,7 +509,7 @@ export default class MessageComposerInput extends React.Component {
  if (this.state.isRichtextEnabled) {
  contentHTML = HtmlUtils.stripParagraphs(
  RichText.contentStateToHTML(contentState),
  - );
  + ).replace(/\<br\>\n/g, '<br>');
  } else {
  const md = new Markdown(contentText);
  if (md.isPlainText()) {
  