Fixes a number of CVEs:
- a DNS request hijacking vulnerability. (CVE-2017-0902)
- an ANSI escape sequence vulnerability. (CVE-2017-0899)
- a DoS vulnerability in the query command. (CVE-2017-0900)
- a vulnerability in the gem installer that allowed a malicious gem to overwrite arbitrary files. (CVE-2017-0901)
Having a separate rubygems package can lead to split-brain scenarios.
Since rubygems is designed to replace himself on a ruby installation,
let's do that.
