Add Object.freeze on private enums

Improve code readability

src/gossipSeed.js

@@ -1,6 +1,8 @@
-module.exports = function GossipSeed(endPoint, hostName) {
+function GossipSeed(endPoint, hostName) {
   if (typeof endPoint !== 'object' || !endPoint.host || !endPoint.port) throw new TypeError('endPoint must be have host and port properties.');
   this.endPoint = endPoint;
   this.hostName = hostName;
   Object.freeze(this);
-};
+}
+
+module.exports = GossipSeed;