Bad submodule url in main feedstocks repo

I tried to `git clone --recursive https://github.com/conda-forge/feedstocks` and it ran into an error on `setuptools_markdown`.

The entry in `.gitmodules` is

```
[submodule "setuptools_markdown"]
path = feedstocks/setuptools_markdown
url = https://github.com/conda-forge/setuptools_markdown-feedstock.git
branch = refs/heads/master
```

but this repository is all dashes, no underscores.

Inspect the .gitmodules entry for setuptools_markdown and compare its URL with the repository name shown in the issue. Verify the correction by retrying the recursive clone of https://github.com/conda-forge/feedstocks; done means the setuptools_markdown submodule resolves successfully.

Written by the indexing model from the issue text.