`RxSwift` dependency in Cartfile changed to `2.6`, which supports Swift 2.3
`RxSwift` dependency in Cartfile changed to `2.6`, which supports Swift 2.3

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