Make sourceApplication nullable
Make sourceApplication nullable

- Matches related declaration in @protocol UIApplicationDelegate

Feverup/braintree_ios,billCTG/braintree_ios,braintree/braintree_ios,braintree/braintree_ios,braintree/braintree_ios,Feverup/braintree_ios,Feverup/braintree_ios,apascual/braintree_ios,apascual/braintree_ios,apascual/braintree_ios,billCTG/braintree_ios,Feverup/braintree_ios,billCTG/braintree_ios,billCTG/braintree_ios,apascual/braintree_ios,billCTG/braintree_ios,braintree/braintree_ios