Gemfile ruby version operators break docker image name

[benjaminwood]

Regarding:

railsdock/lib/railsdock/commands/install.rb

Line 73 in 061c455

::Bundler.definition.ruby_version.versions[0] || RUBY_VERSION

When the Gemfile has defined a ruby version such as: ruby "~> 2.7", an invalid ruby image tag will be used in the compose file. Perhaps we should strip ~> from it.

Version operators are documented here: https://bundler.io/gemfile_ruby.html