Update documentation, so that it does not become outdated whenever a new version of Node is released.

Test on the current version of Node, so we can spot problems early, but don't claim to support it as current release line sometimes introduces bugs, which are later fixed by Node itself.

Fixes karma-runner#3728

Node 17+ changed the DNS resolution (see nodejs/node#40702), so now it resolves `localhost` according to the OS settings instead of IPv4-address first. The Karma server only listens on IPv4 address (127.0.0.1) by default, but the requests are sent to `localhost` in several places and `localhost` is resolved into IPv6 address (`::`) in Node 17+. So the run/stop/proxy request is unable to reach the Karma server and produces an error. This commit configures karma to use the IPv4-address first approach in newer Node version as well.

In the future major release, we may consider changing defaults to listen on IPv6 address instead, but IPv6 is not supported in Docker on macOS and Windows, so I think we should not rush such a change to make sure karma works there out of the box.

Fixes karma-runner#3730