title: InvalidArgumentException in Manager.php line 90: Driver [linkedin] not supported
body: <p>I'm trying to get work with <strong>social authentication</strong> using liknedin provider in Laravel 5.1 but it's giving me that exception.
   I have implemented such authentication  using "github" and "google" providers,but this one sounds weird regarding  <strong>linkedin provider is built-in in Laravel 5.1</strong></p>
  
  <p>This is my redirect function</p>
  
  <blockquote>
  <pre><code>      public function redirectToProvider($provider)
       {
         return Socialite::driver($provider)-&gt;redirect();
       }
  </code></pre>
  </blockquote>
  
  <p>and  my setting</p>
  
  <blockquote>
  <pre><code>  'linkedin' =&gt; [
      'client_id' =&gt;env('LinkedIn_APP_ID'),
      'client_secret' =&gt; env('LinkedIn_APP_SECRET'),
      'redirect' =&gt;     'http://localhost:88/laravel/public/social/login/linkedin',
     ]
  </code></pre>
  </blockquote>