Add 2.3.5 and 2.4.2

[cabello]

These releases contain security fixes.

https://www.ruby-lang.org/en/news/2017/09/14/ruby-2-4-2-released/
https://www.ruby-lang.org/en/news/2017/09/14/ruby-2-3-5-released/

Please and thank you 😃

[tbsvttr]

+1

[mbrinkme]

+1

[wirsslinger]

+1

[yosifkit]

The automated update.sh job is currently running (see the bottom of the readme). Once that finishes we can make the PR to official images.

Duplicate issues: #152 #153 #154 #156 #157.