Fix token color customization for CodeRay >= 1.1.0

CodeRay has recently changed the way terminal token colors are defined (https://github.com/rubychan/coderay/commit/e2acec3ef141725d2fc264e56d1aa18e838c6acf). They are now pre-escaped ANSI strings.

The current customizations in pryrc cause problems when running Pry with CodeRay >= 1.10 (https://github.com/pry/pry/issues/1012#issuecomment-29213405)