Problem with copy/paste from word.

Hello,

When we copy a nested list form the editor to word it works correctly. But if we copy back the list from word to the editor, the nested element are not working (this can be tester on the demo of editor js).

After some digging, this is because the HTML paste into the editor is incorrect. It looks like this :
```

• Coffee


• Tea




• Black tea

Instead of this :
```

• Coffee


• Tea
  
  
  
  • Black tea
  
  
  
  

The problem is that the sub `ul` tag is not inside the `li` tag. For now I discovered the problem only with Word but there might be the problem with other copy paste. I think fixing this might be a good idea to make the copy/paste more resilient.

To fix this we can a code that fixes the HTML before calling the pasteHandler.

I'll make a pull request/