update kivy to 2.3.1

Author: Fak3

pythonforandroid/recipes/kivy/__init__.py

@@ -22,7 +22,7 @@ def is_kivy_affected_by_deadlock_issue(recipe=None, arch=None):
 
 
 class KivyRecipe(CythonRecipe):
-    version = '2.3.0'
+    version = '2.3.1'
     url = 'https://github.com/kivy/kivy/archive/{version}.zip'
     name = 'kivy'