Make node --harmony bin/cake test pass on Node 9

[rdeforest]

Make classMaker() explicitly return an object

Without this change, node --harmony bin/cake test the test "classes with value'd constructors" fails because classMaker returns a number.

[rdeforest]

Should I also add

• node --harmony ./bin/cake test

to appveyor.yml?

[GeoffreyBooth]

We should add Node 9 for both AppVeyor and Travis. And harmony as one of the test commands we run. If harmony tests fail in Node < 9, then we should have harmony only run for Node 9 (because why would someone run an old version of Node in harmony mode?).

[GeoffreyBooth]

P.S. See https://github.com/jashkenas/coffeescript/pull/4880/files

[rdeforest]

Seeing my Cakefile patch in use in #4880 was the best birthday present I got yesterday. :)

Back on topic, harmony tests are currently passing for me on v6 and v8. I agree in principle that there's little to no customer value in making bleeding-edge features tests run and/or pass on non-bleeding-edge runtimes, but until they actually fail I propose that they could serve as a kind of canary-in-a-coal-mine for other surprises. They might reveal obscure changes in older runtimes, dependencies or invalid assumptions in our feature tests.