message: Use same link style in HTML messages
  Links in HTML messages were missing the usual underline style, making them
  look different from links in text messages (which already do this).
  Fixes vector-im/riot-web#4655.
diff: @@ -446,6 +446,7 @@ limitations under the License.
  .mx_EventTile_content .markdown-body a {
  color: $accent-color-alt;
  + text-decoration: underline;
  }
  .mx_EventTile_content .markdown-body .hljs {
  