Node v15.1.0

[kriszyp]

node-abi is incorrectly reporting an ABI version of 84 instead of 88 for Node v15. I assume #95 fixes this as well, but this should further emphasize the need to get that merged.

[vecerek]

Yes, the PR fixes the ABI for Node v15, as well.

[MarshallOfSound]

Fixed in #95