Replace div with span as they are not valid inside of a button element

Author: mmistakes

_layouts/default.html

@@ -15,7 +15,7 @@
     <div class="sidebar-toggle-wrapper">
       <button class="toggle navicon-button larr" type="button">
         <span class="sidebar-toggle-label">{{ site.data.theme.t.menu | default: 'Menu' }}</span>
-        <div class="navicon"></div>
+        <span class="navicon"></span>
       </button>
     </div>
 

docs/_layouts/default.html

@@ -15,7 +15,7 @@
     <div class="sidebar-toggle-wrapper">
       <button class="toggle navicon-button larr" type="button">
         <span class="sidebar-toggle-label">{{ site.data.theme.t.menu | default: 'Menu' }}</span>
-        <div class="navicon"></div>
+        <span class="navicon"></span>
       </button>
     </div>