Create sourcemap in instrumented files

[schutm]

If invoked with nyc instrument it wasn's possible to attach the sourcemap. This created problems for me in the coverage reports created.

[bcoe]

@schutm I'm not sure what the best solution is here such that you and @vanduynslagerp don't consistently break each-other's use-cases.

Is there a heuristic approach we could use so that both your applications of shouldInstrument work? I think we should make an effort to add a test for both so that we don't keep flip-flopping on this feature.

[schutm]

Agreed we shouldn't break each other changes, and test-cases should be there. However since this is in the CLI I didn't think it would break the previous changes.

For now seems I had a dangling comma; which I'll fix

[coveralls]

Changes Unknown when pulling be893c5 on schutm:master into ** on istanbuljs:master**.

[bcoe]

@schutm I think this accidentally reverts https://github.com/istanbuljs/nyc/pull/667/files which would break @vanduynslagerp's use-case.

[coveralls]

Changes Unknown when pulling 6f83f56 on schutm:master into ** on istanbuljs:master**.

[schutm]

@bcoe I removed the accidentally included index.js, which reverted #667. In addition I tidied the commits up to a single one.

[bcoe]

@schutm this looks great 👍 sorry that this took so long to land.

[bcoe]

@schutm try this out, and let me know if it does the trick:

npm i nyc@next --save-dev