CURLOPT_MAX_RECV_SPEED_LARGE(3) on macOS

The text 6a5e3cb9fb8e, as macOS 10.12.5, macOS 10.12.4, macOS 10.12.3, macOS 10.12.2 shipped it.

rate limit data download speed

CURLOPT_MAX_RECV_SPEED_LARGE(3) on macOS now