Events api doesn't use constructor values

When calling the events api, none of the values passed into the constructor are included

EG given two api objects:

```
owned_api = GhApi(username='gone', token=github_token)
global_api = GHApi(token=github_token)
```

I would expect these two calls to be equivalent:

```
owned_api.list_events()
global_api.list_events(username='gone')
```

But get them to be the same, I need to pass the username into both list_events calls.