Wrong number of watchers

I quickly tested this exporter and found that the number of watchers is wrong.
Stars is ok, but gitea has 133 watchers. :wink: 
```
github_repo_watchers{private="false",repo="gitea",user="go-gitea"} 2527.0
github_repo_stars{private="false",repo="gitea",user="go-gitea"} 2527.0
```