Fix Webpack global scope issue

In webpack 4 (Angular 8) the `_global = ...` will return undefined causing "Cannot read property WebSocket of undefined"

Author: giacomodeliberali

lib/browser.js

@@ -1,4 +1,9 @@
-var _global = (function() { return this; })();
+var _global = (function () {
+	if (!this && typeof global !== 'undefined') {
+		return global;
+	}
+	return this;
+})();
 var NativeWebSocket = _global.WebSocket || _global.MozWebSocket;
 var websocket_version = require('./version');