correct grid class mention in docs

docs/docs.html

@@ -1896,7 +1896,7 @@ For example, <code>&lt;section&gt;</code> should be wrapped as inline.
 {% endhighlight %}
 
     <h3 id="forms-control-sizes">Control sizing</h3>
-    <p>Use relative sizing classes like <code>.input-large</code> or match your inputs to the grid column sizes using <code>.span*</code> classes.</p>
+    <p>Use relative sizing classes like <code>.input-large</code> or match your inputs to the grid column sizes using <code>.col-span-*</code> classes.</p>
 
     <h4>Relative sizing</h4>
     <p>Create larger or smaller form controls that match button sizes.</p>