This communicates more clearly for which versions of Node.js
the tests have run.
8 is not listed because tests are failing due to the nock HTTP mocking
library being incompatible with Node v8.
Notes:
- npm run test also runs the memory tests, which might be flaky on
some systems.
- npm run test-coverage only runs the unit tests (it can't run the
memory test anyway because the memory tests create a Node child
process, and istanbul cannot cover that).
