Fixed typo in spec.

--HG--
extra : convert_revision : svn%3Afdd8eb12-d10e-0410-9acb-85c331704f74/trunk%402796

dlib/gui_widgets/widgets_abstract.h

@@ -629,7 +629,7 @@ namespace dlib
 // ----------------------------------------------------------------------------------------
 // ----------------------------------------------------------------------------------------
 
-    class text_box : public drawable
+    class text_box : public scrollable_region 
     {
         /*!
             INITIAL VALUE