Add missing div tag to coding guidelines, a=chris

diff --git a/en-US/pages/coding.thtml b/en-US/pages/coding.thtml
index 288239f..81bafb8 100755
--- a/en-US/pages/coding.thtml
+++ b/en-US/pages/coding.thtml
@@ -1405,3 +1405,4 @@ machinelog_element, a=chris
     </li>

     <p><a href="#toc">Return to table of contents</a>.</p>
+</div>