Dynamically detect v4/v6

[mkg20001]

By default an IPv6-only socket is created which makes it impossible to use this server with IPv4 hosts.
I've added a bit of code that checks the IP version via regex and creates the appropriate socket for it

[zbjornson]

Node.js's "net" module (since v0.3.0) has this ability built in, no need for the regexes:

const net = require("net");
const ipversion = net.isIP(address);
if (ipversion === 0) throw new TypeError("address is neither valid v4 or v6");
const fam = ipversion === 4 ? "udp4" : "upd6";

https://nodejs.org/api/net.html#net_net_isip_input

---

edit This library already uses that actually:

node-named/lib/validators.js

Lines 57 to 62 in 2b1adaa

	IPv4: function(v) {
	return net.isIPv4(v);
	},
	IPv6: function(v) {
	return net.isIPv6(v);
	},

---

edit 2 #26 and #29 make an equivalent fix using the net module.

[zbjornson]

(I think this will match the socket's type, but you could also make this rinfo.family === "IPv6" ? 'udp6' : "udp4".)