Attribute Error about rio-hist

[tomwang221812]

I modify utils.py line 17 from:
if src.mask_flags[0] & MaskFlags.per_dataset:
to
if MaskFlags.per_dataset in src.mask_flag_enums[0]:
and it works on my own datasets now.

Python version : Python 3.6.6 :: Anaconda custom (64-bit)
Rasterio version : 1.0.21
GDAL version : 2.4.0

I was able to get data set 2 to work using these commands.

rio edit-info --nodata null source2.tif
rio edit-info --nodata null reference2.tif

[GeoCG]

@tomwang221812 Your solution solved the issue I had. Thanks a lot !

[sgillies]

Closing in favor of #17. No date set yet.