doc: fix family default value in socket.connect

Documentation says that default value is 4, but in code no any default value: https://github.com/nodejs/node/blob/d3b10f66bd4943f7da9aa25415ea6900d7f48086/lib/net.js#L942

as result dns.lookup uses own default -- 0.

Checklist

• make -j4 test (UNIX), or vcbuild test (Windows) passes
• documentation is changed or added
• commit message follows commit guidelines