minor bug in stream_power.py
minor bug in stream_power.py

Needed to apply a maximum only on a given axis at ln 255.

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