Fix doc of preflow-push maxflow algorithm
Fix doc of preflow-push maxflow algorithm

https://github.com/networkx/networkx/pull/1082#issuecomment-38911845

nathania/networkx,goulu/networkx,debsankha/networkx,harlowja/networkx,ghdk/networkx,blublud/networkx,michaelpacer/networkx,kernc/networkx,tmilicic/networkx,chrisnatali/networkx,ionanrozenfeld/networkx,debsankha/networkx,OrkoHunter/networkx,jakevdp/networkx,bzero/networkx,RMKD/networkx,sharifulgeo/networkx,dhimmel/networkx,SanketDG/networkx,kernc/networkx,ionanrozenfeld/networkx,nathania/networkx,ionanrozenfeld/networkx,bzero/networkx,cmtm/networkx,ghdk/networkx,jakevdp/networkx,farhaanbukhsh/networkx,ltiao/networkx,andnovar/networkx,chrisnatali/networkx,farhaanbukhsh/networkx,chrisnatali/networkx,blublud/networkx,jcurbelo/networkx,jni/networkx,sharifulgeo/networkx,JamesClough/networkx,blublud/networkx,harlowja/networkx,kernc/networkx,harlowja/networkx,dmoliveira/networkx,aureooms/networkx,aureooms/networkx,Sixshaman/networkx,wasade/networkx,NvanAdrichem/networkx,aureooms/networkx,RMKD/networkx,sharifulgeo/networkx,nathania/networkx,dmoliveira/networkx,jni/networkx,beni55/networkx,yashu-seth/networkx,farhaanbukhsh/networkx,debsankha/networkx,ghdk/networkx,jfinkels/networkx,jakevdp/networkx,dhimmel/networkx,dmoliveira/networkx,RMKD/networkx,bzero/networkx,dhimmel/networkx,jni/networkx