doc: fix broken links in n-api doc

- fix 2 broken links
- fix capitalization in description of
napi_create_array-with-length

PR-URL: https://github.com/nodejs/node/pull/12889


Reviewed-By: Sakthipriyan Vairamani <thechargingvolcano@gmail.com>
Reviewed-By: Refael Ackermann <refack@gmail.com>
Reviewed-By: Colin Ihrig <cjihrig@gmail.com>
Reviewed-By: Luigi Pinca <luigipinca@gmail.com>
Reviewed-By: Daniel Bevenius <daniel.bevenius@gmail.com>
Reviewed-By: MichaëZasso <targos@protonmail.com>
Reviewed-By: Gibson Fahnestock <gibfahn@gmail.com>
Reviewed-By: Hitesh Kanwathirtha <digitalinfinity@gmail.com>