CURLOPT_PROXYPORT(3) on macOS

The text 2b27bd458f66, as macOS 10.12.5, macOS 10.12.4, macOS 10.12.3, macOS 10.12.2, macOS 10.12.1, macOS 10.12 shipped it.

port number the proxy listens on

CURLOPT_PROXYPORT(3) on macOS now