typo fix from Jay Z

lectures/gui/index.html

@@ -126,7 +126,7 @@ <h2>Building a GUI</h2>
 <p>
 A scene graph can also be created in advance using the <a
 href="https://www.oracle.com/technetwork/java/javase/downloads/javafxscenebuilder-info-2157684.html">
-JavaFX SceneBuilder application</a>. SceneBuilder saves the scene is saved in
+JavaFX SceneBuilder application</a>. SceneBuilder saves the scene in
 XML format in an <tt>.fxml</tt> file, which can be loaded by the application to
 create the entire scene graph at once.
 </p>