changed Gtk3 -> GKT3 in list of interactive backends.

Author: jrjohansson

lib/matplotlib/rcsetup.py

@@ -26,7 +26,7 @@
 
 interactive_bk = ['GTK', 'GTKAgg', 'GTKCairo', 'FltkAgg', 'MacOSX',
                   'QtAgg', 'Qt4Agg', 'TkAgg', 'WX', 'WXAgg', 'CocoaAgg',
-                  'Gtk3Cairo', 'Gtk3Agg']
+                  'GTK3Cairo', 'GTK3Agg']
 
 
 non_interactive_bk = ['agg', 'cairo', 'emf', 'gdk',