Update Dockerfile

1 job for master in 3 minutes and 57 seconds (queued for 2 seconds)
Name Stage Failure
build Build
Missing required packages: ruby
RVM autolibs is now configured with mode '2' =>
'Allow RVM to use package manager if found, fail if dependencies are missing. This is default.',
please run `rvm autolibs enable` to let RVM do its job or run and read `rvm autolibs [help]`
or visit https://rvm.io/rvm/autolibs for more information.
Requirements installation failed with status: 1.
The command '/bin/bash -lc rvm install 2.6.6 && rvm alias create 2.6 ruby-2.6.6 && rvm use --default 2.6.6' returned a non-zero code: 1
Cleaning up file based variables
ERROR: Job failed: exit code 1