Add next-auth

Github: https://github.com/iaincollins/next-auth
My fork for docs: https://github.com/ndom91/next-auth

Will most likely consolidate the two, but the now.sh URL will stay the same, so no changes will be required from js.org side.

cnames_active.js

@@ -1328,6 +1328,7 @@ var cnames_active = {
   "newbyte": "newbytee.github.io/newbyte",
   "newyear": "dndrbots.github.io/new_year_counter",
   "next": "zeit.github.io/next-site",
+  "next-auth": "next-auth-docs.now.sh",
   "nexus": "nexusjs.netlify.com",
   "nflow": "nflow-js.github.io", // noCF? (don´t add this in a new PR)
   "nfwyst": "nfwyst.github.io",