Updated library to work with latest Alamofire/AFNetworking. Updated travis yml to build with latest Xcode

[csknns]

Update codebase to work with latest Alamofire (5.6.2).
The main fixes are that Alamofire expects the calls to the session delegate to happen on the same queue as the one the initial session has started, but the NSURLSession-Mock always uses the main queue.

An other fix to work with Alamofire is that it expects the didFinishCollecting of the URLSessionTaskDelegate to be called, see the new URLSessionTaskMetrics APIs.
So I updated the MockEntry.swift to call the metrics API, before the task is finished.

      DispatchQueue.current.asyncAfter(deadline: .now() + time) {
            if #available(iOS 10.0, *) {
                let metrics = URLSessionTaskMetrics()
                // Alamofire waits for the didFinishCollecting to trigger the callbacks of a request
                delegate.urlSession?(session, task: task, didFinishCollecting: metrics)

Updated travis yml to install the latest stable cocoapods instead of the latest beta (--pre), this fixes failing travis CI builds due to pod lint checks.
Also removed the unnecessary framework search path "$(SDKROOT)/Developer/Library/Frameworks" that caused this warning: