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

* See also: https://github.com/svenfuchs/i18n/commit/92b57b1e4f84adcdcc3a375278f299274be62445

gems/i18n/CVE-2013-4492.yml

+---
+gem: i18n
+cve: 2013-4492
+osvdb: 
+url: https://groups.google.com/forum/#!topic/ruby-security-ann/pLrh6DUw998
+title: i18n missing translation error message XSS
+date: 2013-12-03
+
+description: |
+  The HTML exception message raised by I18n::MissingTranslation fails
+  to escape the keys.
+
+cvss_v2: 
+
+patched_versions:
+  - ~> 0.5.1
+  - >= 0.6.6