Fixed doctest for fixed_link_ids.
Fixed doctest for fixed_link_ids.

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