private void adjustBottomByAspectRatio(RectF rect, float aspectRatio) {
    rect.bottom = rect.top + rect.width() / aspectRatio;
  }
Adjust bottom edge by current crop window width and the given aspect ratio, the top edge
remains in possition while the top adjusts to keep aspect ratio to the width.
core/src/main/java/com/theartofdev/edmodo/cropper/CropWindowMoveHandler.java