Update quickstart.rst macOS brew cask command
Update quickstart.rst macOS brew cask command

-brew cask install
+brew install --cask
kivy/python-for-android,PKRoma/python-for-android,kivy/python-for-android,kronenpj/python-for-android,kivy/python-for-android,kivy/python-for-android,kronenpj/python-for-android,kronenpj/python-for-android,kivy/python-for-android,PKRoma/python-for-android,kronenpj/python-for-android,kronenpj/python-for-android,PKRoma/python-for-android,PKRoma/python-for-android,PKRoma/python-for-android