Fixed doctest for valid field groups.
Fixed doctest for valid field groups.

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