[Markdown] Nested bulleted lists don't work in Julia Markdown

I have some function documentation that looks like this:

```
* ABC
   * ABC-1
   * ABC-2
   * ABC-3
* DEF
* GHI
```

I expect it to render like this:
- ABC
  - ABC-1
  - ABC-2
  - ABC-3
- DEF
- GHI

But it actually renders like this:
- ABC
- ABC-1
- ABC-2
- ABC-3
- DEF
- GHI
