Fix some issues with relative URLs on Github Pages.

docs/templates/shared/_header.liquid

@@ -7,12 +7,12 @@
         <span class="icon-bar"></span>
         <span class="icon-bar"></span>
       </button>
-      <a class="brand" href="/">jq</a>
+      <a class="brand" href="{{root}}/">jq</a>
       <div class="nav-collapse collapse">
         <ul class="nav">
           {% for item in navigation %}
             <li {% if item.permalink == permalink %} class="active" {% endif %}>
-              <a href="{{item.permalink}}">{{item.name}}</a>
+              <a href="{{root}}{{item.permalink}}">{{item.name}}</a>
             </li>
           {% endfor %}
           <li><a href="https://github.com/stedolan/jq/issues">Issues</a></li>