doc,n-api: fix `introduced_in` metadata

Node.js v7.10.0 did not contain N-API. Update the `introduced_in`
metadata to prevent a broken 7.x "View another version" link in the
N-API docs.

PR-URL: https://github.com/nodejs/node/pull/27745


Reviewed-By: Ruben Bridgewater <ruben@bridgewater.de>
Reviewed-By: Luigi Pinca <luigipinca@gmail.com>
Reviewed-By: Michael Dawson <michael_dawson@ca.ibm.com>
Reviewed-By: Trivikram Kamat <trivikr.dev@gmail.com>
Reviewed-By: Rich Trott <rtrott@gmail.com>
Reviewed-By: Anna Henningsen <anna@addaleax.net>