[FEATURE/FIX] Move from analytics.js to gtag.js (Google Analitics V4)

[davorpa]

Hi

A new version of Google Analitics has released, V4, and scripting block has changed.

Documentation Guide: https://developers.google.com/analytics/devguides/collection/gtagjs/migration

It will be a good point to change this lines for new ones provided by guide.

hacker/_layouts/default.html

Lines 37 to 46 in 7b7303a

	{% if site.google_analytics %}
	<script>
	(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','//www.google-analytics.com/analytics.js','ga');
	ga('create', '{{ site.google_analytics }}', 'auto');
	ga('send', 'pageview');
	</script>
	{% endif %}

Of course, mantaining backwards compatibility using some site property indicating the mode to load.

Are you agree?

[davorpa]

At least in other themes was updated. For example, in caiman:

https://github.com/pages-themes/cayman/blob/1bcabf8e4c139d46ebe0678998059db53f670caf/_layouts/default.html#L5-L13

[davorpa]

Modularized at #79