title: Cannot find module '@firebase/app-types/private' - Firebase throws error
body: <p>I am working on application using angular and  firebase. I installed firebase with the instructions given on site and the versions as follows,</p>
  
  <pre><code>"angularfire2": "^5.0.0-rc.4",
  "firebase": "^4.8.1",
  </code></pre>
  
  <p>but the following error comes </p>
  
  <blockquote>
    <p>ERROR in
    node_modules/@firebase/database/dist/esm/src/api/Database.d.ts(4,33):
    error TS2307: Cannot find module '@firebase/app-types/private'. 
    node_modules/@firebase/database/dist/esm/src/core/AuthTokenProvider.d.ts(17,39):
    error TS2307: Cannot find module '@firebase/app-types/private'.</p>
  </blockquote>