Updates docs for CakeTime::format().

Related ticket: https://cakephp.lighthouseapp.com/projects/42648/tickets/3854-cookbook-caketime-docs-incorrect

Related commits: 0d013f8da5a80bae69e0a5375d3a2971b09a9db4 and a2c2902dd60bb8a51edb264f2686ed96a63bdf92