[security] Remove reference to Node Security Project

The Node Security Platform service no longer exists. New security
advisories will be published to GitHub Security Advisories.

Author: lpinca

SECURITY.md

@@ -25,8 +25,9 @@ following methods:
 
 Once we have acknowledged receipt of your report and confirmed the bug ourselves
 we will work with you to fix the vulnerability and publicly acknowledge your
-responsible disclosure, if you wish. In addition to that we will report all
-vulnerabilities to the [Node Security Project](https://nodesecurity.io/).
+responsible disclosure, if you wish. In addition to that we will create and
+publish a security advisory to
+[GitHub Security Advisories](https://github.com/websockets/ws/security/advisories).
 
 ## History