Fix 404 link to fastify-cookie plugin and replace http link

[davidcralph]

Just two small things I found when setting up the module, @fastify/cookie link was invalid and the npm.im link was slow(er) to load due to having to redirect from http to https.

Checklist

• run npm run test and npm run benchmark
• tests and/or benchmarks are included
• documentation is changed or added
• commit message and code follows the Developer's Certification of Origin
  and the Code of conduct

[mcollina]

lgtm