setup depfu to keep dependencies up-to-date

[m5o]

Hey @rafaelfranca 👋

Of curse, this is a demo application but what do you think setup depfu with some clicks to automatically receive dependency and relevant security updates. I volunteer to check the incoming updates.

Heroku would also support automatic deploys, this would be a nice addition.

• 📝 https://devcenter.heroku.com/articles/github-integration#automatic-deploys

[rafaelfranca]

I forgot to setup automatic deploys, just did. I also enabed dependabot.