add trailing slash automatically for private docker repositories

hello, i'm running self-hosted hexus for private docker registry.

This extensions tries REPO_URL/v2 for API endpoint, but Nexus by default returns http/404 for "/v2" url.

Work-around is to add this

```
rewrite ^(\/v2)$ $1/ permanent;
```

in nginx.

But, is there any chance that this extension will probe REPO_URL/v2/ (with trailing slash) as well?