doc/pisa-en.html: s/marign/margin/

doc/pisa-en.html

@@ -161,7 +161,7 @@ <h2>Pages and Frames </h2>
 </pre>
 <p>To define more frames just add some more <code>@frame</code> blocks. You may use the following properties to define the dimensions of the frame:</p>
 <ul>
-  <li><code>marign</code></li>
+  <li><code>margin</code></li>
   <li><code>margin-top</code></li>
   <li><code>margin-left</code></li>
   <li><code>margin-right</code></li>