Change required ruby version to >=2.0.0

[csabiftw]

We have recently ran into the problem of not being able to install the fluentd-plugin-systemd gem which depends on the serverengine gem.

The machines we use run CentOS 7, for which the default ruby version available is 2.0.0.

While I have seen the discussion around the commit which bumped the required version to the current one, I would like to add a few points:

• while 2.0.0 may not be maintained anymore, it still is the current officially available ruby version for CentOS 7, and possibly other distributions too
• the official ruby lang site does not specify a version, but refers you to using your package manager or in general trusts you to choose your version otherwise (https://www.ruby-lang.org/en/documentation/installation/#yum)
• enforcing a ruby version requirement in a gem that other gems depend on, and in turn possibly breaking their updates / new installs is not ideal

While it would be possible to fork the project and maintain the fork, or take on the task of updating ruby on our machines, I feel like this would be better handled by the proposed change, or the removal of the constraint.

All my points assume that the project does not use any >=2.1.0 specific features.

[tagomoris]

The constraint >= 2.1 is to allow to use Ruby features specific in >= 2.1 (e.g., keyword arguments without default values, String#scrub, Socket#getifaddrs and so on). That is the only way NOT to break the compatibility by using these features in any releases of 2.x.

[repeatedly]

One way is using scl repository: https://www.softwarecollections.org/en/scls/rhscl/rh-ruby23/ or use ruby-build to install latest version.