In RH2019, new ui, parse error when trying to configure Google Analytics with my RH project

I have added the following code to the header of the master page:

<!-- Global site tag (gtag.js) - Google Analytics -->
<script async src="https://www.googletagmanager.com/gtag/js?id=UA-000000000-0" ></script>
<script>
window.dataLayer = window.dataLayer || [];
function gtag(){dataLayer.push(arguments);}
gtag('js', new Date());

gtag('config', 'UA-000000000-0');

</script>

where UA-000000000-0 is my Google Analytics Tracking ID.

And Robohelp is giving me a parse error for the first line of the script saying invalid character s and underlining the s of the src. I tried adding it this way 

<script src="https://www.googletagmanager.com/gtag/js?id=UA-000000000-0" async ></script>

(as I found a website that seemed to suggest that you add the async at the end) but then got Invalid character > underlining the > next to async. 

I got this code from the Google Analytics website.