Convert sets to lists in doctests for Python 3.
Convert sets to lists in doctests for Python 3.

cmshobe/landlab,SiccarPoint/landlab,Carralex/landlab,landlab/landlab,laijingtao/landlab,laijingtao/landlab,landlab/landlab,cmshobe/landlab,RondaStrauch/landlab,ManuSchmi88/landlab,cmshobe/landlab,SiccarPoint/landlab,RondaStrauch/landlab,landlab/landlab,amandersillinois/landlab,csherwood-usgs/landlab,decvalts/landlab,ManuSchmi88/landlab,Carralex/landlab,ManuSchmi88/landlab,csherwood-usgs/landlab,RondaStrauch/landlab,decvalts/landlab,amandersillinois/landlab,Carralex/landlab