Minor fix to #523 for dropCursor

#523 - Changed the dropCursor behavior to be more consistent with undo/redo.

```
if(dragAction.toBefore && !wb.matches(dragAction.toBefore, '.block')) {
           	// Sometimes the "next sibling" ends up being the cursor
           	dragAction.toBefore = dragAction.toBefore.nextElementSibling;
}
```
This block doesn't seem to do anything; dragAction.toBefore.nextElementSibling appears to always be null. Might need additional clarification as to what it's for.