Add PromiseKit dependency

- Added PromiseKit dependency

Carthage/Checkouts/PromiseKit/Sources/after.m

@@ -0,0 +1,14 @@
+#import "AnyPromise.h"
+@import Dispatch;
+@import Foundation.NSDate;
+@import Foundation.NSValue;
+
+/// @return A promise that fulfills after the specified duration.
+AnyPromise *PMKAfter(NSTimeInterval duration) {
+    return [AnyPromise promiseWithResolverBlock:^(PMKResolver resolve) {
+        dispatch_time_t time = dispatch_time(DISPATCH_TIME_NOW, (int64_t)(duration * NSEC_PER_SEC));
+        dispatch_after(time, dispatch_get_global_queue(0, 0), ^{
+            resolve(@(duration));
+        });
+    }];
+}