Changed doctests to use isinstance.
Changed doctests to use isinstance.

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