message: Add attachment without 's' to make outgoing
diff: @@ -658,7 +658,7 @@ export class BotkitConversation<O extends object = {}> extends Dialog<O> {
  // This could be extended to include cards and other activity attributes.
  } else {
  // if there is text, attachments, or any channel data fields at all...
  - if (line.type || line.text || line.attachments || (line.channelData && Object.keys(line.channelData).length)) {
  + if (line.type || line.text || line.attachments || line.attachment || (line.channelData && Object.keys(line.channelData).length)) {
  await dc.context.sendActivity(await this.makeOutgoing(dc, line, step.values));
  } else if (!line.action) {
  console.error('Dialog contains invalid message', line);
  