Add the "true" value to the allowfullscreen attribute

to make localized sites parser happy and not complain about bad xml attributes

_includes/about.html

@@ -39,7 +39,7 @@ <h3>Imperative and reactive code</h3>
       <h2>The inspiration behind Quarkus...</h2>
     </div>
     <div class="width-6-12 width-12-12-m video-container">
-      <iframe src="https://www.youtube.com/embed/SQDR34KoC-8" title="Quarkus why, how and what by Emmanuel Bernard" frameborder="0" allow="autoplay; encrypted-media" allowfullscreen></iframe>
+      <iframe src="https://www.youtube.com/embed/SQDR34KoC-8" title="Quarkus why, how and what by Emmanuel Bernard" frameborder="0" allow="autoplay; encrypted-media" allowfullscreen="true"></iframe>
     </div>
     <div class="width-6-12 width-12-12-m">
       <p>For more about the why, how and what of Quarkus, check out the Devoxx Belgium presentation where Quarkus 1.0 was released in November 2019.</p>