Running create_spacenet_masks.py gives AttributeError: module 'apls_utils' has no attribute 'get_road_buffer'

```apls_utils.py``` only have ```_get_road_buffer``` function, after I rename it to ```get_road_buffer```, I can run this script to generate RGB image and mask, but the generated mask image is pure dark, which means there is no label information on it. Can anyone help me?