hosts overview: create thead in same way as for domain overview (fixes small visual difference)

nsupdate/main/templates/main/overview.html

@@ -6,7 +6,14 @@
         <div class="col-lg-12">
             <h3>Your Hosts</h3>
             <table class="table">
-            <tr><th>Host</th><th>IPv4 Address</th><th>IPv6 Address</th><th>Comment</th></tr>
+            <thead>
+                <tr>
+                    <th>Host</th>
+                    <th>IPv4 Address</th>
+                    <th>IPv6 Address</th>
+                    <th>Comment</th>
+                </tr>
+            </thead>
             {% for host in hosts %}
                 <tr>
                     <td><a href="{% url 'host_view' host.pk %}"><b>{{ host.subdomain }}.{{ host.domain.domain }}</b></a></td>