"Warning: date(): It is not safe to rely on the system's timezone settings."

[Erik Mulder]

Hi folks,

I get a warning on my website without me making any changes. The warning is : "Warning: date(): It is not safe to rely on the system's timezone settings. You are *required* to use the date.timezone setting or the date_default_timezone_set() function. In case you used any of those methods and you are still getting this warning, you most likely misspelled the timezone identifier. We selected the timezone 'UTC' for now, but please set date.timezone to select your timezone. in - See more at: ..." 

I retraced this warning to the following script:

<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', 'XXXXXXXX', 'auto');

  ga('send', 'pageview');

</script>

Is it correct to change it here to the suggested function :  date_default_timezone_set()  

By the way, what caused the change?

Thx

Erik