Update docs to use discord (#284)

Author: graceg-stripe

CONTRIBUTING.md

@@ -10,8 +10,9 @@ represent bugs with React Stripe.js, not Stripe.js itself.
 
 If you're having general trouble with Stripe.js or your Stripe integration,
 please reach out to us using the form at <https://support.stripe.com/email> or
-come chat with us at #stripe on freenode. We're very proud of our level of
-service, and we're more than happy to help you out with your integration.
+come chat with us on the [Stripe Discord server][developer-chat]. We're very
+proud of our level of service, and we're more than happy to help you out with
+your integration.
 
 If you've found a bug in React Stripe.js, please [let us know][issue]! You may
 also want to check out our [issue template][issue-template].
@@ -70,3 +71,4 @@ passing any of these checks will cause the CI build to fail.
 [elements]: https://stripe.com/elements
 [issue]: https://github.com/stripe/react-stripe-js/issues/new
 [issue-template]: .github/ISSUE_TEMPLATE.md
+[developer-chat]: https://stripe.com/go/developer-chat