Exclude .DS_Store from release

Currently you `.DS_Store` file is being included in the release.

```
curl --silent -L  https://files.pythonhosted.org/packages/source/c/cmd2/cmd2-4.3.0.tar.gz | tar tfz - | grep DS
cmd2-4.3.0/docs/.DS_Store
```

Author: traylenator

MANIFEST.in

@@ -5,4 +5,4 @@ recursive-include docs *
 prune .github
 prune build
 exclude .github .gitignore .readthedocs.yaml
-global-exclude htmlcov/** .coverage* __pycache__/** .gitignore
+global-exclude htmlcov/** .coverage* __pycache__/** .gitignore .DS_Store