Bad url when using multiple providers
Hi :)

I have an app with multiple provider buttons for login (github and google for instance).
1. If I open a private session and try google it works.
2. If I open a private session and try github it works.
3. If I open a private session and try google, then logout, then try github: it fails for github.
4. If I open a private session and try github, then logout, then try google: it fails for google.

As you can see here, in scenario 4.:
![Capture d’écran 2020-07-21 à 18 01 50](https://user-images.githubusercontent.com/11708220/88078099-52937480-cb7c-11ea-9b2c-1c4a475462f1.png)

Google redirected to `/connect/google/callback` (witch is good)
And then grant fails and redirects me to `/connect/github/success` instead of `/connect/google/success`.

My grant configuration is

```javascript
{
  google:
   { enabled: true,
     icon: 'google',
     key:
      '4blablablabla4i.apps.googleusercontent.com',
     secret: 'gq2_blablablamUBqs',
     callback: 'http://localhost:3000/connect/google/success',
     scope: [ 'email' ],
     redirect_uri: 'https://75fa70e635a9.ngrok.io/connect/google/callback',
  },
  github:
   { enabled: true,
     icon: 'github',
     key: 'a2d6cblablabla3df48be',
     secret: 'a264e428815dablablabla348a2c3',
     callback: 'http://localhost:3000/connect/github/success',
     scope: [ 'user', 'user:email' ],
     redirect_uri: 'https://75fa70e635a9.ngrok.io/connect/github/callback' },
}
```

It feels like a session/cookie problem. I'm not an expert in it. Do you thing Grant has an issue or that the issue is more likely on my side?

Thanks for your help :)
Pierre