Require Node 18+

[EvanHahn]

Node 16 is no longer supported. Helmet v8 should drop support too.

Required subtasks:

• Update the engines field of package.json
• Remove old Node versions from CI configuration (bbcefa3)
• Update the changelog

[njmulsqb]

Hi @EvanHahn,

I am willing to work on this, can you tell me how much effort is required on this?

I have contributed to this package in the past: #354

[EvanHahn]

The required subtasks are written in the description. I estimate <30 minutes of work.

Please make your change against the v8.0.0 branch. Let me know if I can help with anything!

[njmulsqb]

Alright, can I get my NPM account under "Collaborators" on https://www.npmjs.com/package/helmet after working on this issue?

[EvanHahn]

I don't usually add people there, but I add lots of people to the contributors list on the Helmet website. Feel free to add your name there after you make your change!

[EvanHahn]

Completed in #450. Thanks, @njmulsqb!