Make piwik code async

site/layouts/partials/foot.html

@@ -1,5 +1,5 @@
    </div>
-   <script src="/res/script/piwik.js" integrity="sha384-m2EXauJIeXunnu9rWV0uaFjwoSeSA+jEbAKdI5sQaGiiiOwht/hOVB/8lq2JI8Bd"></script>
+   <script async src="/res/script/piwik.js" integrity="sha384-m2EXauJIeXunnu9rWV0uaFjwoSeSA+jEbAKdI5sQaGiiiOwht/hOVB/8lq2JI8Bd"></script>
    <noscript><p><img src="//a.c5h.io/piwik.php?idsite=1&amp;rec=1" style="border:0;" alt="" /></p></noscript>
   </body>
 </html>