Added libpng to anaconda install
Added libpng to anaconda install

jshoyer/plantcv,stiphyMT/plantcv,AntonSax/plantcv,jshoyer/plantcv,danforthcenter/plantcv,danforthcenter/plantcv,stiphyMT/plantcv,AntonSax/plantcv,stiphyMT/plantcv,danforthcenter/plantcv