docs(README): add `power-assert message does not appear in Node8`
docs(README): add `power-assert message does not appear in Node8`

refs: https://github.com/power-assert-js/power-assert/issues/85

falsandtru/power-assert,twada/power-assert,twada/power-assert,power-assert-js/power-assert,power-assert-js/power-assert,falsandtru/power-assert