[minor] fix upson logo & url

Author: smnandre

ux.symfony.com/templates/_footer.html.twig

@@ -38,10 +38,10 @@
                     <span class="d-block d-md-inline">
                         hosted with
                         <span style="font-weight: 700;">
-                            <a href="https://platform.sh"
-                               rel="external noopener noreferrer"
+                            <a href="https://upsun.com"
+                               rel="external"
                                style="font-weight: 700;"
-                            >Platform.sh</a>
+                            >Upsun</a>
                         </span>
                     </span>
                 </p>