Added what little information I could find for i18n's CVE-2013-4492.

* See also: https://github.com/svenfuchs/i18n/commit/92b57b1e4f84adcdcc3a375278f299274be62445
Merge pull request #58 from rubysec/CVE-2013-4492

Added what little information I could find for i18n's CVE-2013-4492.