refactor with async/await

Trying to be more robust about error handling and failure.

lib/BindingAgent.js

@@ -1,6 +1,6 @@
-var http = require('http');
-var util = require('util');
-var assert = require('assert');
+import http from 'http';
+import util from 'util';
+import assert from 'assert';
 
 // binding agent will return a given options.socket as the socket for the agent
 // this is useful if you already have a socket established and want the request
@@ -20,4 +20,4 @@ function create_connection(port, host, options) {
     return this.socket;
 }
 
-module.exports = BindingAgent;
+export default BindingAgent;