(v6.x backport) doc types fixes
This is a backport for these commits:
https://github.com/nodejs/node/commit/ff1361957df58ef92c8a9dfce40c6091ea3a21d4 https://github.com/nodejs/node/commit/9be03a2903a0196212868d9e4282d638355828e7 https://github.com/nodejs/node/commit/172be50fe173ee24cdfec8b5cb2b54b28f74557a https://github.com/nodejs/node/commit/5f32024055adc2f908c582d933259f9fcf5db423
cc: @MylesBorins