Updated minimum required Xcode version
Updated minimum required Xcode version

Since only Swift 2.2+ is supported, only Xcode 7.3+ can be used.
ibm-bluemix-mobile-services/bms-clientsdk-swift-core,ibm-bluemix-mobile-services/bms-clientsdk-swift-core,ibm-bluemix-mobile-services/bms-clientsdk-swift-core