Updating dependencies and using functional components to finish the app.

[pmaher]

This updates the app to use the latest version of apollo client which has changed quite a bit since the start of this tutorial. Changed all class components to be functional components with hooks. Also, to run the app you'll need to add a /server/config/keys.js file of this form so that you don't have your credentials checked into github: module.exports = { username: 'your-db-username', password: 'your-db-password' };