docs: use ES6 import in TypeScript README example (webpack-contrib#140)

Updates the TypeScript example to use the ES6 import syntax like the other examples. Includes the change to `Worker.ts` mentioned in webpack-contrib#111 to get it to work with `import` instead of `require`.

README.md

@@ -174,7 +174,7 @@ declare module "worker-loader!*" {
     constructor();
   }
 
-  export = WebpackWorker;
+  export default WebpackWorker;
 }
 ```
 
@@ -191,7 +191,7 @@ ctx.addEventListener("message", (event) => console.log(event));
 
 **App.ts**
 ```typescript
-import Worker = require("worker-loader!./Worker");
+import Worker from "worker-loader!./Worker";
 
 const worker = new Worker();