Github user alpinegizmo commented on the issue:
https://github.com/apache/flink/pull/5395
It would be lovely to ditch ruby 1.9. However, if I understand correctly,
we don't fully control the environment that builds the docs, and the last time
we tried this we couldn't get a newer ruby there. But it has been a while, and
maybe the ASF infrastructure folks have seen the light. @rmetzger Can we
somehow determine what ruby version is running on the build machines? ---
