swap ms out

[gurgunday]

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

[jsumners]

Can you provide some justification for this change?

[gurgunday]

Sure, many Fastify plugins have moved to this version of ms [1].

The main justification is consistency among the core plugins, it is supposed to be faster too, which is why it was adopted in the first place.

[1] (a) — https://github.com/fastify/send/blob/cf190d743d9ea07be0eab5f66b8793297c773858/package.json#L28
[1] (b) — https://github.com/fastify/fastify-jwt/blob/1aa4790668924572cca664d12b657b7d4e9f1dab/package.json#L35

[mcollina]

lgtm