update MANIFEST.in to fix kivy#3320

Author: cbenhagen

MANIFEST.in

@@ -4,4 +4,4 @@ recursive-include examples *
 recursive-include kivy/data *.png *.jpg *.ttf *.kv *.fs *.vs *.json *.gif *.atlas *.ico
 recursive-include kivy/tools *.png *.txt *.bat *.sh *.py
 recursive-include kivy/tests *.py *.png
-recursive-include kivy *.pyd *.pyx *.c *.pxi *.h *.pxd
+recursive-include kivy *.pyd *.pyx *.c *.pxi *.h *.pxd *.m