Fix docker setup for newer or updated image builds

[chocoelho]

Checklist

• I have read the Contribution & Best practices Guide.
• My branch is up-to-date with the upstream master branch.
• The tests pass locally with my changes.
• I have added tests that prove my fix is effective or that my feature works(if appropriate).
• I have added necessary documentation (if appropriate).

Short description of what this resolves/which issues does this fix?:

• OSEM Installation using Docker doesn't work #2511

Changes proposed in this pull request:

• Add OSEM_RUBY_VERSION as build argument to Docker setup

[AndrewKvalheim]

Curious to hear your thoughts on this vs. #2646, which look like two different attempts at solving the same problem.

[chocoelho]

Curious to hear your thoughts on this vs. #2646, which look like two different attempts at solving the same problem.

I just wanted to kept the existent approach as using OSEM_RUBY_VERSION. This change would make it possible to configure this variable at build time.

[hennevogel]

The variable really is only valuable if you want to use another ruby version. The docker build failed because the underlying OS changed.