script tag in index.html

Hi,

we are in the process of enabling our ember app for fastboot. So far it works very well when using `ember serve`, but it's not yet working with fastboot-app-server: We have a script tag in our index.html to load google analytics as suggested from google at https://developers.google.com/analytics/devguides/collection/analyticsjs/

```html

(function(i,s,o,g,r,a,m){i['GoogleAnalyticsObject']=r;i[r]=i[r]||function(){
(i[r].q=i[r].q||[]).push(arguments)},i[r].l=1*new Date();a=s.createElement(o),
m=s.getElementsByTagName(o)[0];a.async=1;a.src=g;m.parentNode.insertBefore(a,m)
})(window,document,'script','https://www.google-analytics.com/analytics.js','ga');

ga('create', 'UA-XXXXX-Y', 'auto');

```

When using `ember server` we can then later on access the ga object as `window.ga` but when accessing the page via fastboot-app-server, this results in `TypeError: window.ga is not a function`. Can you help me fix this or just indicate where I missed something in the docs? I would be very grateful for your help!