Only compute user/repo if suggesting badges for GitHub (#1601)
Only compute user/repo if suggesting badges for GitHub (#1601)

This resolves the following error occurring in production:

```
TypeError: Cannot read property 'slice' of null
/home/m/shields/lib/suggest.js in findSuggestions at line 40:33
  const userRepo = url.pathname.slice(1).split('/');
```
badges/shields,badges/shields,badges/shields