The `FALSY_VALUE_REJECTION` error code added by
https://github.com/nodejs/node/pull/12712 did not have the `ERR_` prefix,
nor was it added to the errors.md documentation. Add the prefix in for
consistency.
PR-URL: https://github.com/nodejs/node/pull/13604
Reviewed-By: Luigi Pinca <luigipinca@gmail.com>
Reviewed-By: Timothy Gu <timothygu99@gmail.com>
Reviewed-By: Gibson Fahnestock <gibfahn@gmail.com>
Reviewed-By: Anna Henningsen <anna@addaleax.net>
Reviewed-By: Refael Ackermann <refack@gmail.com>
Reviewed-By: Colin Ihrig <cjihrig@gmail.com>
Reviewed-By: Benjamin Gruenbaum <benjamingr@gmail.com>