Fixes Issue with Newlines between nested lists.

Basically the issue is that when you have a nested list:

    - Item
      - Item 1
      - Item 2

And you save that in Geeknote. When you open it again you get:

    - Item

      - Item 1
      - Item 2

Note the separation between the two.

The reason for this to happen, is that Evernote adds a `<p>` inside the li that
has a nested `<ul>` element. The above commit just removes that `<p>` so that
html2text outputs some correct markdown.