doc: DEFAULT_ECDH_CURVE was added in 0.11.13

Document this with the YAML meta-data.

PR-URL: https://github.com/nodejs/node/pull/10983


Reviewed-By: Colin Ihrig <cjihrig@gmail.com>
Reviewed-By: Gibson Fahnestock <gibfahn@gmail.com>
Reviewed-By: Luigi Pinca <luigipinca@gmail.com>