ImplementingUndoHistory.md: improve formatting
ImplementingUndoHistory.md: improve formatting

ptkach/redux,ellbee/redux,JoeStanton/redux,tappleby/redux,doerme/redux,neighborhood999/redux,conorhastings/redux,tatsuhino/reactPractice,gajus/redux,bvasko/redux,bvasko/redux,dieface/redux,roth1002/redux,joaomilho/redux,chentsulin/redux,tatsuhino/reactPractice,camsong/redux,jas-chen/typed-redux,mjw56/redux,Aweary/redux,jas-chen/redux,okmttdhr/redux-with-comment,CompuIves/redux,roth1002/redux,chentsulin/redux,javascriptjedi/redux-select,ssk7833/redux,joaomilho/redux,gaearon/redux,ide/redux,tappleby/redux,edge/redux,jas-chen/typed-redux,ptkach/redux,mjw56/redux,jdlehman/redux,andreieftimie/redux,joshwreford/idle-game,gaearon/redux,lifeiscontent/redux,neighborhood999/redux,mikekidder/redux,paulkogel/redux,splendido/redux,naoishii/ohk2016C,joshwreford/idle-game,keyanzhang/redux,lifeiscontent/redux,Aweary/redux,splendido/redux,doerme/redux,tappleby/redux,leoasis/redux,CompuIves/redux,jas-chen/redux