fix version (flutter#3399)

Author: Chris Yang

packages/image_picker/image_picker/pubspec.yaml

@@ -2,7 +2,7 @@ name: image_picker
 description: Flutter plugin for selecting images from the Android and iOS image
   library, and taking new pictures with the camera.
 homepage: https://github.com/flutter/plugins/tree/master/packages/image_picker/image_picker
-version: 0.6.7+20
+version: 0.6.7+21
 
 flutter:
   plugin: