Add missing update to header.html from last commit

Author: lefticus

_includes/header.html

@@ -46,6 +46,9 @@
         <li {% if page.url == '/support.html'%} class='active' {% endif %}>
         <a href="/support.html">Support</a>
         </li>
+        <li {% if page.url == '/coding_standards.html'%} class='active' {% endif %}>
+        <a href="/coding_standards.html">Coding Standards</a>
+        </li>
         <li>
         <a href="https://travis-ci.org/ChaiScript/ChaiScript"><img src="https://travis-ci.org/ChaiScript/ChaiScript.png?branch=develop"/></a>
         </li>