message: use correct name when mentioning
diff: @@ -141,7 +141,7 @@ export class MessageProcessor {
  const id = results[1];
  const member = msg.guild.members.get(id);
  const memberId = `@_discord_${id}:${this.opts.domain}`;
  - const memberStr = member ? member.user.username : memberId;
  + const memberStr = member ? (member.nickname ? member.nickname : member.user.username) : memberId;
  content = content.replace(results[0], memberStr);
  results = USER_REGEX.exec(content);
  }
  @@ -156,7 +156,7 @@ export class MessageProcessor {
  const memberId = escapeHtml(`@_discord_${id}:${this.opts.domain}`);
  let memberName = memberId;
  if (member) {
  - memberName = escapeHtml(member.user.username);
  + memberName = escapeHtml(member.nickname ? member.nickname : member.user.username);
  }
  const memberStr = `<a href="${MATRIX_TO_LINK}${memberId}">${memberName}</a>`;
  content = content.replace(results[0], memberStr);
  