fix table border bug with double borders on theads and use of colgroup

docs/base-css.html

@@ -435,6 +435,10 @@ For example, <code>section</code> should be wrapped as inline.
   <div class="row">
     <div class="span8">
       <table class="table table-bordered table-striped">
+        <colgroup>
+          <col class="span1">
+          <col class="span7">
+        </colgroup>
         <thead>
           <tr>
             <th>Tag</th>