Make rubocop version configurable

[woidda]

It would really helpful to specify the rubocop version and the needed plugins.

In the entrypoint.sh shell script the version of the rubocop and the plugins + versions is hard coded. Would it be possible to iterate over let's say all provided environment variables and use the string they provided as version?

env:
  RUBOCOP: "0.80.1"
  RUBOCOP_RSPEC: "1.38.1"
  RUBOCOP_PERFORMANCE: "1.5.2"
  RUBOCOP_RAILS: "2.4.2"

maybe

for var in "${!RUBOCOP@}"; do
    # substitute _ with -
    org="${var//[_]/_}"
    # compose the command an convert the enviroment var key to lower case
    # build a comand similar to: gem install rubocop -v 0.80.1 
    COMMAND=$(printf 'gem install %s -v %s\n' "${org,,}" "${!var}")
    # execute the command
    eval $COMMAND
done

Should do the trick.

I think code-climate has the same issue with a not supported graphql plugin for rubocop. This would really awesome to have that supported here.