fix typo in comment: leapflog -> leapfrog (react-grid-layout#387)

Author: nikolas

lib/utils.js

@@ -291,7 +291,7 @@ export function moveElementAwayFromCollision(layout: Layout, collidesWith: Layou
   }
 
   // Previously this was optimized to move below the collision directly, but this can cause problems
-  // with cascading moves, as an item may actually leapflog a collision and cause a reversal in order.
+  // with cascading moves, as an item may actually leapfrog a collision and cause a reversal in order.
   return moveElement(layout, itemToMove, undefined, itemToMove.y + 1);
 }