title: Can't find variable: Expo
body: <p>I am making an app with react native. It has login with facebook option, it keeps giving me this error. "Facebook Login Error: Can't find variable: Expo"
  What am I doing wrong here?</p>
  
  <p>Do I have to install some dependencies on Linux </p>
  
  <pre><code>f.auth().onAuthStateChanged(function(user) {
    if(user){
      //logged in
      console.log('Logged in', user);
    }else {
      //logged out
      console.log('logged out');
    }
  });
  
  
  
  const { type, token} = await Expo.Facebook.logInWithReadPermissionsAsync(
    'APP_ID',
    { permissions: ['email', 'public_profile'] }
  );
  
  if(type === 'success'){
    const credential = firebase.auth.FacebookAuthProvider.credential(token);
      firebase.auth().signInWithCredential(credential).catch((error) =&gt; {
      console.log('Error...',error);
    })
  }
  
  
  
  
  
  
  
  
  Possible Unhandled Promise Rejection (id:0): ReferenceError: Can't find variable: Expo loginWithFacebook$
  </code></pre>