limit "engines" to <8

[refack]

With the introduction of async-hooks in v8.x, there should be a way to do this without process.binding('async_wrap');

[coveralls]

Coverage remained the same at 100.0% when pulling f0f5b01 on refack:patch-1 into 7ea43ea on bucharest-gold:master.

[lance]

@refack thanks for the contribution - and apologies for the latency. This is a back-burner project for me. 👍

[refack]

Just trying to limit the use of process.binding('async_wrap'); in the wild.