main/ruby: Correct wrong CVE number in secfixes for version 2.6.6-r0
See upstream's release notes: https://www.ruby-lang.org/en/news/2020/03/31/ruby-2-6-6-released/
Edited by Daniel Néri
See upstream's release notes: https://www.ruby-lang.org/en/news/2020/03/31/ruby-2-6-6-released/