Made changes to allow macOS 10.12 support

Source/Manager.swift

@@ -344,9 +344,11 @@ public class Manager {
 
             - parameter session: The session that no longer has any outstanding requests.
         */
+#if !os(OSX)
         public func urlSessionDidFinishEvents(forBackgroundURLSession session: URLSession) {
             sessionDidFinishEventsForBackgroundURLSession?(session)
         }
+#endif
 
         // MARK: - NSURLSessionTaskDelegate
 

Source/Upload.swift

@@ -281,7 +281,14 @@ extension Manager {
         encodingMemoryThreshold: UInt64 = Manager.MultipartFormDataEncodingMemoryThreshold,
         encodingCompletion: ((MultipartFormDataEncodingResult) -> Void)?)
     {
-        DispatchQueue.global(attributes: DispatchQueue.GlobalAttributes.qosDefault).async {
+
+        let attributes: DispatchQueue.GlobalAttributes
+        if #available(OSXApplicationExtension 10.10, *) {
+            attributes = DispatchQueue.GlobalAttributes.qosDefault
+        } else {
+            attributes = []
+        }
+        DispatchQueue.global(attributes: attributes).async {
             let formData = MultipartFormData()
             multipartFormData(formData)