Typo fix.
Typo fix.

Example is showing how to make a ``Cell`` a ``DropTarget``, but description talks about "drag source".
tylercollier/react-dnd-demo,numso/react-dnd,srajko/react-dnd,jgable/react-dnd,randrianov/react-dnd,globexdesigns/react-dnd,wagonhq/react-dnd,globexdesigns/react-dnd,tylercollier/react-dnd-demo,tomulin1/react-dnd,numso/react-dnd,longlho/react-dnd,jgable/react-dnd,randrianov/react-dnd,tomulin1/react-dnd,longlho/react-dnd,wagonhq/react-dnd,srajko/react-dnd