CodeRay::Encoders::Ruby is not defined; you must load it first.
Now it is loaded: CodeRay::Scanners::Ruby
See?
Require is also possible: CodeRay::Scanners::C
See?
Now load some mapped scanners: cpp and plain.
Require all Scanners:
[[:c, CodeRay::Scanners::C], [:cpp, :c], [:delphi, CodeRay::Scanners::Delphi], [:irb, :ruby], [:pascal, :delphi], [:plain, CodeRay::Scanners::Plaintext], [:plaintext, CodeRay::Scanners::Plaintext], [:ruby, CodeRay::Scanners::Ruby]]