* refactors arn? method out
  * found bug in README
  * adds deprecation comment
  * updates front-end docs to explain ARN

https://github.com/github/github-services/blob/master/CONTRIBUTING.md

Favor `until` over `while` for negative conditions and Favor modifier `while/until` usage when you have a single-line body. https://github.com/bbatsov/ruby-style-guide#syntax

Empty strings are truthy and may be passed as a payload in production and would
be converted to 0, resulting in a non-working default port. The tests passed
when nil was used in the test environment.