Add PromiseKit dependency

- Added PromiseKit dependency

Carthage/Checkouts/PromiseKit/Extensions/StoreKit/Sources/SKReceiptRefreshRequest+Promise.swift

@@ -0,0 +1,35 @@
+#if !PMKCocoaPods
+import PromiseKit
+#endif
+import StoreKit
+
+extension SKReceiptRefreshRequest {
+    public func promise() -> Promise<SKReceiptRefreshRequest> {
+        return ReceiptRefreshObserver(request: self).promise
+    }
+}
+
+private class ReceiptRefreshObserver: NSObject, SKRequestDelegate {
+    let (promise, seal) = Promise<SKReceiptRefreshRequest>.pending()
+    let request: SKReceiptRefreshRequest
+    var retainCycle: ReceiptRefreshObserver?
+    
+    init(request: SKReceiptRefreshRequest) {
+        self.request = request
+        super.init()
+        request.delegate = self
+        request.start()
+        retainCycle = self
+    }
+    
+    
+    func requestDidFinish(_: SKRequest) {
+        seal.fulfill(request)
+        retainCycle = nil
+    }
+    
+    func request(_: SKRequest, didFailWithError error: Error) {
+        seal.reject(error)
+        retainCycle = nil
+    }
+}