fix: ReferenceError: window is not defined (#319)

* set output.globalObject = "this" in webpack.umd.config.babel.js

fixes error with webpack umd output. see issue #318

* fix lint

Author: hkennyv

webpack.umd.config.babel.js

@@ -7,6 +7,7 @@ const umdConfig = Object.assign({}, baseConfig, {
   },
 
   output: {
+    globalObject: "this",
     path: path.resolve(__dirname, "build"),
     publicPath: "/",
     filename: "[name].js",