Add setKeepAlive for net.socket

* Prevent `Error: read ECONNRESET` when using net.socket by using
setKeepAlive when connecting.
* Use an `initialDelay` of 60 seconds.

Net -> socket.setKeepAlive:
https://nodejs.org/api/net.html#net_socket_setkeepalive_enable_initialdelay

Closes #38, #41

lib/winston-logstash.js

@@ -199,6 +199,7 @@ Logstash.prototype.connect = function () {
     this.socket.connect(self.port, self.host, function () {
       self.announce();
       self.connecting = false;
+      self.socket.setKeepAlive(true, 60 * 1000);
     });
   }
 
@@ -243,4 +244,4 @@ Logstash.prototype.sendLog = function (message, callback) {
 
 Logstash.prototype.getQueueLength = function () {
   return this.log_queue.length;
-};
+};