Rails ActiveSupport::TimeZone MAPPING constant value is missing

[DevDocs](https://devdocs.io/rails~5.0/activesupport/timezone)

[Rails Docs](http://api.rubyonrails.org/classes/ActiveSupport/TimeZone.html)

See the "Constants" section of each. DevDocs references the MAPPING constant but it's missing the value of the constant, which is a big hash.