title: Namespace 'firebase' has no exported member 'firestore'
body: <p>Just started using AngularFire2 v5 seeing the following error about a dozen times when I run the app: Namespace 'firebase' has no exported member 'firestore' in the following .d.ts files:</p>
  
  <pre><code>node_modules/angularfire2/firebase.app.module.d.ts
  node_modules/angularfire2/firestore/collection/changes.d.ts
  node_modules/angularfire2/firestore/firestore.d.ts
  node_modules/angularfire2/firestore/interfaces.d.ts
  node_modules/angularfire2/firestore/observable/fromRef.d.ts
  </code></pre>
  
  <p>I'm on "angularfire2": "^5.0.0-rc.3".</p>