[css-text-3] Markup fix

Author: fantasai

css-text-3/Overview.bs

@@ -1019,7 +1019,7 @@ Text Processing</h3>
 
   <table class="data">
     <colgroup class="header"></colgroup>
-    <colgroup span=4></colgroup>
+    <colgroup span=5></colgroup>
     <thead>
       <tr>
         <th></th>