Add missing closing div element

src/invidious/views/template.ecr

@@ -106,7 +106,7 @@
 
             <%= content %>
 
-            <div id="placeholder" style="margin: 8em;"/>
+            <div id="placeholder" style="margin: 8em;"></div>
             <div class="footer">
                 <div class="pure-g">
                     <div class="pure-u-1 pure-u-md-1-3">