Update v8.x docs for http request set timeout

[jbunton-atlassian]

When upgrading from Node.js 8 to 10 I hit the behaviour change in #8895. This documentation update would have helped me find the problem faster :)

Also see #25121 for an update to the docs on master.

Thanks :)

Checklist

• documentation is changed or added
• commit message follows commit guidelines

[mscdex]

I think you meant to target the v8.x-staging branch instead?

[jbunton-atlassian]

@mscdex so sorry! Indeed, I forgot to look at the diff 🤦‍♂️

[mscdex]

I'm not sure adding this is worthwhile. We already have changelogs with both commit info and high-level change information as well as important API changes across versions in the most recent docs.

[jbunton-atlassian]

It took me a few hours to find this. The current documentation for v8.x is wrong which meant I actually only found the issue through a git-bisect. I was hoping to save others the same effort.

[mscdex]

I see, I was mainly referring to the part about 'Note that this behaviour changes in Node.js version 9 and higher.'

[jbunton-atlassian]

Ack... I'm failing at git today.

See #25123.