Node engine V8 compatibility is broken

[Borewit]

ts-node is no longer work on Node V8, because yn is enforcing Node V10 compatibility.
Caused by: yn#26

The motivation for changing the V8 requirement to V10 is because Node.js V8 is no longer supported. I believe node engine requirement should indicate the engine(s) the module works with.

[cspotcode]

I'm going to try wrapping the old version of yn in a wrapper that converts null return values to undefined. That should achieve the desired behavior without upgrading yn, which avoids the problematic engine requirement.

[cspotcode]

We can also add a yarn invocation to the test suite to catch the incompatibilities.

[cspotcode]

@Borewit @Darep yarn --ignore-engines should let you install in the meantime.

Our tests run on node 6 so everything should work once you get past the package manager.