Making SessionDelegate final

Source/Alamofire.swift

@@ -345,7 +345,7 @@ public class Manager {
     /**
         Responsible for handling all delegate callbacks for the underlying session.
     */
-    public class SessionDelegate: NSObject, NSURLSessionDelegate, NSURLSessionTaskDelegate, NSURLSessionDataDelegate, NSURLSessionDownloadDelegate {
+    public final class SessionDelegate: NSObject, NSURLSessionDelegate, NSURLSessionTaskDelegate, NSURLSessionDataDelegate, NSURLSessionDownloadDelegate {
         private var subdelegates: [Int: Request.TaskDelegate]
         private let subdelegateQueue = dispatch_queue_create(nil, DISPATCH_QUEUE_CONCURRENT)
         private subscript(task: NSURLSessionTask) -> Request.TaskDelegate? {