support doing coverage even in node_modules
support doing coverage even in node_modules

The --cov argument was looking at global.__coverage__, which is fine
in tests of this module, or when linked, but when installed as a dep,
and run via an npm test script, it would fail to realize that coverage
was loaded.

Specify in a cli flag to the child process.

strongloop-forks/node-tap,jkrems/node-tap,evanlucas/node-tap,tapjs/node-tap,jkrems/node-tap,othiym23/node-tap,iarna/node-tap,othiym23/node-tap,tapjs/node-tap,myndzi/node-tap,isaacs/node-tap,evanlucas/node-tap,jinivo/marhert,isaacs/node-tap,iarna/node-tap,strongloop-forks/node-tap,myndzi/node-tap