title: Can't add Autofac to ServiceCollection in .Net Core
body: <p>I want to add Autofac to .Net Core application. 
  I've tried to do all steps from <a href="http://autofaccn.readthedocs.io/en/latest/integration/aspnetcore.html#quick-start-with-configurecontainer" rel="nofollow noreferrer">Autofac:Getting started tutorial</a>, I've installed <code>Autofac.Extensions.DependencyInjection</code>, have updated <code>Program</code> class, but can't add autofac as in example.</p>
  
  <p>Get error </p>
  
  <blockquote>
    <p>Error CS1061  'IServiceCollection' does not contain a definition for
    'AddAutofac' and no extension method 'AddAutofac' accepting a first
    argument of type 'IServiceCollection' could be found (are you missing
    a using directive or an assembly reference?)</p>
  </blockquote>
  
  <p>Reinstall nuget package, clean &amp; rebuild solution, close VS - things which doesn't help. </p>
  
  <hr>
  
  <pre><code>public class Program
  {
    public static void Main(string[] args)
    {
          var host = new WebHostBuilder()
              .UseKestrel()
              .ConfigureServices(services =&gt; services.AddAutofac()) //here is problem
              .UseContentRoot(Directory.GetCurrentDirectory())
              .UseIISIntegration()
              .UseStartup&lt;Startup&gt;()
              .Build();
  
          host.Run();
    }
  }
  </code></pre>
  
  <hr>
  
  <p>Version of Autofac - 4.6.2
  Version of Autofac.Extensions.DependencyInjection - 4.2.0</p>