chore: remove support for node 6

[lusarz]

This pull request remove support for node v6.

Let me know if I missed something here ...

[johnjbarton]

Please describe the breaking change (and our reasons):
http://karma-runner.github.io/3.0/dev/git-commit-msg.html

We also need to have a similar change to the integration-tests project, and land it before any async changes.

[lusarz]

@johnjbarton Thank you, I've updated commit message.

What you mean by "integration-tests project" ?

[johnjbarton]

The karma-runner integration tests (tests with plugins) are configured here:
https://github.com/karma-runner/integration-tests/blob/master/.travis.yml
and pulled into the test run via
https://github.com/karma-runner/karma/blob/master/scripts/integration-tests.sh

[johnjbarton]

There is also a documentation line:

https://github.com/karma-runner/karma/blob/f71da205d779e208fcd4bdbcc9e9b35f93994d1f/docs/intro/04-faq.md#which-version-of-nodejs-does-karma-run-with

Maybe we can replace That is 6.x, 8.x and 10.x at this point. with something that acknowledges the version dependency. You may need to install older versions of karma-runner if you must support older versions of nodejs. For example, to run on nodejs 6.x, install karma-runner 3.x. Then in future we can just leave this doc file as is.

[lusarz]

I created pull request on integration-tests project:
karma-runner/integration-tests#10

Yeah, it would be nice to update this documentation line - do you have proposition for whole section ? Because currently it contains Karma works on all LTS versions , which would not be true after this pull request merge.

[johnjbarton]

Karma works on all LTS versions node in active maintenance state (see LTS docs for more info) as well as the latest stable version. That is 6.x, 8.x and 10.x at this point.

to eg:

Karma is tested on (at least) the active LTS versions of node as specified by the
Node.js Release Working Group. The nodejs version numbers are set in the package.json. Older versions of karma work with older versions of nodejs, but these older versions are not maintained or updated.

[lusarz]

Okay, I updated this info in docs.