Fix node-dogstatsd constructor type definition

As per the documentation the `socket` argument to the constructor
is an optional Socket type not a string type. Using a string would
result in a fatal error.

types/node-dogstatsd/index.d.ts

@@ -4,7 +4,10 @@
 //                 Michael Mifsud <https://github.com/xzyfer>
 // Definitions: https://github.com/DefinitelyTyped/DefinitelyTyped
 
+/// <reference types="node" />
+
 declare module "node-dogstatsd" {
+  import * as dgram from 'dgram';
 
   export interface StatsDOptions {
     global_tags?: string[];
@@ -25,7 +28,9 @@ declare module "node-dogstatsd" {
   }
 
   export class StatsD implements StatsDClient {
-    constructor(host: string, port?: number, socket?: string, options?: StatsDOptions);
+    public socket: dgram.Socket
+
+    constructor(host: string, port?: number, socket?: dgram.Socket, options?: StatsDOptions);
 
     timing(stat: string, time: number, sample_rate?: number, tags?: string[]): void;
 

types/node-dogstatsd/node-dogstatsd-tests.ts

@@ -1,12 +1,14 @@
+import * as dgram from 'dgram';
 import * as datadog from 'node-dogstatsd';
 
 function test_statsd_client() {
   // can create client with defaults
   let client = new datadog.StatsD('localhost');
   let options: datadog.StatsDOptions = { global_tags: ['environment:definitely_typed']};
+  const socket: dgram.Socket = dgram.createSocket('udp4');
 
   // can create client with all params
-  client = new datadog.StatsD('localhost', 8125, null, options);
+  client = new datadog.StatsD('localhost', 8125, socket, options);
 
   let key: string = 'key';
   let timeValue: number = 99;