Repo can be cloned with incomplete name

Nobody has claimed this yet.

in Gitman v3.7, if you use only the "repo" parameter and leave out "name" in a `.gitman.yml`, you may end up with a stripped name... for example given this configuration a "ctu-mrs" folder is created even though the repo name is "ctu-mrs.github.io"

```yaml
location: .
sources:
- repo: https://github.com/ctu-mrs/ctu-mrs.github.io.git
rev: master
```

It can be mitigated by specifying a name, in which case the created folder is "ctu-mrs.github.io", matching the repo name

```yaml
location: .
sources:
- name: ctu-mrs.github.io
repo: https://github.com/ctu-mrs/ctu-mrs.github.io.git
rev: master
```

This doesn't match Git's behavior so it must be an issue on Gitman's side

```bash
git clone https://github.com/ctu-mrs/ctu-mrs.github.io.git
Cloning into 'ctu-mrs.github.io'...
...
```

Reproduce the `.gitman.yml` example using only the `repo` parameter and compare the created directory with `git clone` behavior. Trace how Gitman derives a folder name when `name` is omitted; done means the folder uses the full repository name, such as `ctu-mrs.github.io`, without requiring an explicit `name`.

Written by the indexing model from the issue text.