ruby-build 20200214

• Fix TruffleRuby 19.3.0.2 definition

• ruby 2.3 EOL

• use correct key named warn_eol

• remove unavailable jruby versions

• add back withdifferent download source

• add warn_eol

• ruby 2.4 security maintenance

• Add truffleruby-dev

  • Uses the latest nightly, which is automatically built.

• Make sure to install to a clean prefix

  • Otherwise, existing files in the prefix could easily conflict and
    potentially cause very hard to debug errors.
  • This is particularly important for *-dev builds which might be
    repeatedly installed to the same directory.