fix for menu issue

- #33

Author: kalwalt

_includes/header.html

@@ -1,16 +1,16 @@
-<nav class="navbar is-primary" >
+<nav class="navbar is-primary" x-data="{ openNav: false }">
     <div class="container">
         <div class="navbar-brand">
             <a href="{{ site.baseurl }}/" class="navbar-item" style="padding: 0">
               <img id="header-img" style="max-height: 4rem" src="{{site.url}}/resources/webarkit-logo-social.jpg" alt="WebAR Kit logo" title="webarkit.org home"/>
             </a>
-            <a role="button" class="navbar-burger burger" aria-label="menu" aria-expanded="false" data-target="navMenu">
+            <a role="button" class="navbar-burger burger" aria-label="menu" aria-expanded="false" data-target="navMenu" :class="{ 'is-active': openNav }" x-on:click="openNav = !openNav">
                 <span aria-hidden="true"></span>
                 <span aria-hidden="true"></span>
                 <span aria-hidden="true"></span>
             </a>
         </div>
-        <div class="navbar-menu" id="navMenu">
+        <div class="navbar-menu" id="navMenu" :class="{ 'is-active': openNav }">
             <div class="navbar-start">
                 <a href="{{ site.baseurl }}/" class="navbar-item {% if page.url == "/" %}is-active{% endif %}">Home</a>
                 {% if site.data.navigation %}