Fix mistake in replaceChild parameter order in manual

Author: marijnh

manual.html

@@ -75,7 +75,7 @@ <h2 id="usage">Basic Usage</h2>
     textarea with a real editor:</p>
 
     <pre>var myCodeMirror = CodeMirror(function(elt) {
-  myTextArea.parentNode.replaceChild(myTextArea, elt);
+  myTextArea.parentNode.replaceChild(elt, myTextArea);
 }, {value: myTextArea.value});</pre>
 
     <p>However, for this use case, which is a common way to use