How to fix Error Attribute name "async" associated

Someone ask me the question about error when designed Blogger ( Blogspot ) template or add Google Adsense code into your Blogger ( Blogspot ) template. Specifically, the error is: Attribute name "async" associated with an element type "script" must be followed by the ' = ' character.
So, how to fix it ? Just easy and do it step by step with me.
You just need to add the attribute to lack blogger template as needed as follows : 

<script async src='//pagead2.googlesyndication.com/pagead/js/adsbygoogle.js'/>

 Fix it like : 

<script async='async' src='//pagead2.googlesyndication.com/pagead/js/adsbygoogle.js'/>

And done ! Save Template.