Update CONFIG_PATHS in favor of `Lcms::Engine::Engine.root`

[paranoicsan]

There can be places where configuration files are looked in the Rails.root... paths. That need to be changed to Lcms::Engine::Engine.root.

lcms-engine/lib/doc_template.rb

Line 4 in c0e9717

CONFIG_PATH ||= Rails.root.join('config', 'lcms.yml')