Add Ctrl+= for zoom_in

labelme/config/default_config.yaml

@@ -50,7 +50,7 @@ shortcuts:
   open_next: D
   open_prev: A
 
-  zoom_in: Ctrl++
+  zoom_in: [Ctrl++, Ctrl+=]
   zoom_out: Ctrl+-
   zoom_to_original: Ctrl+0
   fit_window: Ctrl+F