Fix test coverage reporting

[johnBartos]

This PR will...

• Exclude the tests folder from Istanbul
• Use the instanbul-instrument-loader
  • Seems to run the same as the other package, but is recommended by the author when using typescipt: https://github.com/mattlewis92/karma-coverage-istanbul-reporter#about
• Bump the Karma version to the next major
  • Fixes a minor security vulnerability
  • Breaking change is dropping Node 6 support
• Removes some extraneous deps

Why is this Pull Request needed?

So that the coverage amount is correctly reported

Are there any points in the code the reviewer needs to double check?

No

Resolves issues:

Checklist

• changes have been done against master branch, and PR does not conflict
• new unit / functional tests have been added (whenever applicable)
• API or design changes are documented in API.md

[itsjamie]

istanbul-api a dependency of the karma-coverage-istanbul-reporter was deprecated by the Istanbul group pretty recently in favor of directly using the istanbul-*. See istanbuljs/istanbuljs#378.

I'm ok with switching back to the other dependency if the other one isn't working, however, if it just wasn't completely configured (included the tests folder in the coverage numbers) then it may save us some time from filing issues or PRs to hopefully get karma-coverage-istanbul-reporter updated to move away from istanbul-api usage in the near future if we stay with the dependency that is already targeting the v3.x dependency line.

[johnBartos]

@itsjamie We have been using the karma-coverage-istanbul-reporter - what I changed was the webpack loader (which does not use the Istanbul API afaik) from https://github.com/JS-DevTools/coverage-istanbul-loader to https://github.com/webpack-contrib/istanbul-instrumenter-loader. Not sure why we were using the former over the latter, considering one has pretty low usage and the other is maintained by people at Webpack.

I'll make the maintainer of the coverage reporter aware of the API changes to see next steps. But it seems like we can use it until we bump Istanbul to the next major.

[itsjamie]

Gotcha. I got lost in all the packages flying around I guess.

Yeah, if they both work sounds good to me.

[johnBartos]

Might be better to switch to a different coverage lib actually. Apparently you need to pay the maintainer of karma-coverage-istanbul-reporter for issue fixes. Going to do a bit more research.