Replace `mock` => `double` in lieu of deprecation

DEPRECATION: mock is deprecated. Use double instead. Called from /Users/pootsbook/Development/gems/sage_one/spec/sage_one_spec.rb:30:in `block (4 levels) in <top (required)>'.
Merge pull request #1 from pootsbook/master

Replace `mock` => `double` due to deprecation