message: Add m.sticker as an expected attachment type
diff: @@ -92,7 +92,13 @@ export class MatrixEventProcessor {
  }
  public async HandleAttachment(event: any, mxClient: any): Promise<string|Discord.FileOptions> {
  - const hasAttachment = ["m.image", "m.audio", "m.video", "m.file"].indexOf(event.content.msgtype) !== -1;
  + const hasAttachment = [
  + "m.image",
  + "m.audio",
  + "m.video",
  + "m.file",
  + "m.sticker",
  + ].indexOf(event.content.msgtype) !== -1;
  if (!hasAttachment) {
  return "";
  }
  