Resolve "Bump rubygems to latest version to address CVE-2017-0903"
Closes #3429
Upstream changelog
=== 2.6.14 / 2017-10-09
Security fixes:
* Whitelist classes and symbols that are in loaded YAML.
See CVE-2017-0903 for full details.
Fix by Aaron Patterson.
Edited by Balasankar 'Balu' C