Documentation tweak.

Author: Nathan Williams

docs/usage.md

@@ -53,7 +53,7 @@ $(function() {
 		<td valign="top">
 			Specifies a RegExp or String containing a regular expression that the current search filter must match to be allowed to be created.  May also be a predicate function that takes the filter text and returns whether it is allowed.</td>
 		<td valign="top"><code>mixed</code></td>
-		<td valign="top"><code>false</code></td>
+		<td valign="top"><code>null</code></td>
 	</tr>
 	<tr>
 		<td valign="top"><code>highlight</code></td>