@Override
  public boolean equals(Object o) {
    return o instanceof MaskTransformation &&
      ((MaskTransformation) o).maskId == maskId;
  }
@param maskId If you change the mask file, please also rename the mask file, or Glide will get
              the cache with the old mask. Because key() return the same values if using the
              same make file name. If you have a good idea please tell us, thanks.
transformations/src/main/java/jp/wasabeef/glide/transformations/MaskTransformation.java