fixed a typo.

git-svn-id: http://anonsvn.jboss.org/repos/javassist/trunk@432 30ef5769-5b8d-40dd-aea6-55b5d6557bb3

tutorial/tutorial.html

@@ -1043,7 +1043,7 @@ adds a new field <code>hiddenValue</code> to <code>java.lang.String</code>:
 <ul><pre>ClassPool pool = ClassPool.getDefault();
 CtClass cc = pool.get("java.lang.String");
 cc.addField(new CtField(CtClass.intType, "hiddenValue", cc));
-pool.writeFile("java.lang.String", ".");</pre></ul>
+cc.writeFile("java.lang.String", ".");</pre></ul>
 
 <p>This program produces a file <code>"./java/lang/String.class"</code>.