Updated python3 testapp ndk-api to 21

Author: inclement

testapps/setup_testapp_python3.py

@@ -4,7 +4,7 @@
 
 options = {'apk': {'requirements': 'sdl2,pyjnius,kivy,python3',
                    'android-api': 27,
-                   'ndk-api': 19,
+                   'ndk-api': 21,
                    'dist-name': 'bdisttest_python3_googlendk',
                    'ndk-version': '10.3.2',
                    'arch': 'armeabi-v7a',