removed lower() on the filename

Author: Phil Elson

lib/matplotlib/backend_bases.py

@@ -2114,7 +2114,7 @@ def get_default_filename(self):
         a default filename.
         """
         default_filename = self.get_window_title() or 'image'
-        default_filename = default_filename.lower().replace(' ', '_')
+        default_filename = default_filename.replace(' ', '_')
         return default_filename + '.' + self.get_default_filetype()
 
     def switch_backends(self, FigureCanvasClass):