message: Fix type error of attachments field
  Fixes `error TS1122: A tuple type element list cannot be empty.`
diff: @@ -33,7 +33,7 @@ interface BotkitMessageTemplate {
  text: string[];
  action?: string;
  quick_replies?: [any];
  - attachments?: [];
  + attachments?: any[];
  channelData?: any;
  collect: {
  key: string;
  