Invalid URL for getRepositoryArchive

Calling method RepositoryApi.getRepositoryArchive
```java
RepositoryApi rapi = api.getRepositoryApi();
rapi.getRepositoryArchive(project.getId(), "HEAD", Constants.ArchiveFormat.ZIP);
```
I get 404 Not found exception, because url looks like:
`https://gitlab.com/api/v4/projects/123/repository/archive/./zip`
instead of
`https://gitlab.com/api/v4/projects/123/repository/archive.zip`