Merge pull request #37 from toxic-johann/master

[fix] fix  duplicate outputs when using with multiple instances of HtmlWebpackPlugin

Author: jeffposnick

demo/client/another.js

@@ -0,0 +1,3 @@
+const h1 = document.createElement('h1');
+h1.innerText = 'I am another page';
+document.body.appendChild(h1);