title: 'User' can't be assigned to the parameter type 'Future<User>' in FutureBuilder
body: <p>I'm trying to determine if user is logged in (Flutter Firebase) using FirebaseAuth.instance.currentUser, and then return LoginScreen or Dashboard, but getting an error. I tried to write code based on instructions from FirebaseFlutter, but those seems to be deprecated...</p>
  <pre><code>  Widget build(BuildContext context) {
      return FutureBuilder&lt;User&gt;(
          future: FirebaseAuth.instance.currentUser,
          builder: (BuildContext context, AsyncSnapshot&lt;User&gt; snapshot) {
            if (snapshot.hasData) {
              User user = snapshot.data;
              /// is because there is user already logged
              return Dashboard();
            }
  
            /// other way there is no user logged.
            return LoginScreen();
          });
    }
  </code></pre>
  <p>I'm getting an error in 3rd line <code>future: ...</code> that stands for <code>The argument type 'User' can't be assigned to the parameter type 'Future&lt;User&gt;'</code>. Please may anyone explain to me how should I do this, and what I'm doing wrong?
  I tried to pass that in function <code>()=&gt;</code> but it still not work...
  Currently using firebase_auth: 0.20 and firebase_core 0.7</p>