Import HexModelGrid in doctests.
Import HexModelGrid in doctests.

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