Change CVE-2016-2339 URL to NVD

Updated the URL for CVE-2016-2339 to point to NVD.

Author: jasnow

rubies/ruby/CVE-2016-2339.yml

@@ -2,7 +2,7 @@
 engine: ruby
 cve: 2016-2339
 ghsa: c4w7-m676-pcvp
-url: https://github.com/advisories/GHSA-c4w7-m676-pcvp
+url: https://nvd.nist.gov/vuln/detail/CVE-2016-2339
 title: Ruby 2.1 has exploitable heap overflow vulnerability
 date: 2017-01-06
 description: |