'branch' includes the next path segment if it's not 'master'

```js
gh('https://github.com/fimbullinter/wotan/tree/master/packages/mimir').branch; // 'master'
gh('https://github.com/fimbullinter/wotan/tree/foo/packages/mimir').branch; // 'foo/packages'
```

Also note that property `path` is not present for non-master branches.
