Updated minimum Python version to 3.6

This should have been the original value, agreed in
kivy#1918

Author: inclement

pythonforandroid/recommendations.py

@@ -189,7 +189,7 @@ def check_ndk_api(ndk_api, android_api):
 
 
 MIN_PYTHON_MAJOR_VERSION = 3
-MIN_PYTHON_MINOR_VERSION = 4
+MIN_PYTHON_MINOR_VERSION = 6
 MIN_PYTHON_VERSION = LooseVersion('{major}.{minor}'.format(major=MIN_PYTHON_MAJOR_VERSION,
                                                            minor=MIN_PYTHON_MINOR_VERSION))
 PY2_ERROR_TEXT = (