Insert a space for aesthetic appeal.

git-svn-id: https://svn.apache.org/repos/asf/ant/core/trunk@278414 13f79535-47bb-0310-9956-ffa450edef68

docs/manual/CoreTasks/concat.html

@@ -158,7 +158,7 @@ Resource Collection</a>s are used to
       <p>The concat task supports nested
         <a href="../CoreTypes/filterchain.html"> FilterChain</a>s.</p>
 
-      <h4>header,footer</h4>
+      <h4>header, footer</h4>
         <p><em>since Ant 1.6</em>.</p>
       <p>Used to prepend or postpend text into the concatenated stream.</p>
       <p>The text may be in-line or be in a file.</p>