Broken Slack link in README/website

Hey there, just discovered quicktype, awesome project!

But I notice the README and the website mention "join us on slack" but point to http://slack.quicktype.io/ which is a currently broken vercel app

```
404: NOT_FOUND
Code: DEPLOYMENT_NOT_FOUND

[slackin-dnnovkeacz.vercel.app might be available. Click here to learn how to assign it to a project.](https://vercel.com/docs/custom-domains#assigning-a-domain-to-a-git-branch)
```

I have no idea how to fix it but I thought you might be interested in knowing this :)