coverage reportDir should respect --cwd

[jl-]

when invoked with nyc --cwd sub-directory, coverage reports were saved in ./coverage, shouldn't it be ./sub-directory/coverage?

[coveralls]

Changes Unknown when pulling 3f85c62 on jl-:patch-1 into ** on istanbuljs:master**.

[JaKXz]

This change makes sense to me, but I don't think we have an existing test case for it. That would be great to add, but thanks for the contribution :)

[bcoe]

@jl- this seems reasonable to me;

[bcoe]

@jl- please try npm i nyc@next, this candidate release should have your changes.