Updated Xcode version in `.travis.yml` file to 8.3
Updated Xcode version in `.travis.yml` file to 8.3

Polidea/RxBluetoothKit,Polidea/RxBluetoothKit,Fitbit/RxBluetoothKit,Fitbit/RxBluetoothKit,Fitbit/RxBluetoothKit,Polidea/RxBluetoothKit