Fix whitespace detection and stripping in getMarkdownFromSlide

[puyo]

I had this code in my slide:

```elixir
defmodule YouTube do
  def search_videos(query) do
    Repo.all(from video in Video,
    where: query in video.search_terms)
  end
end
```

Before:

After:

Similar to #1847 and #1831

[puyo]

Seems fixed now! Thank you!

[ghost]

Whehhahehe