Made Authorizer completion handler @escaping

Author: Brandon Shega

Sources/Authorizer.swift

@@ -1,5 +1,6 @@
 import Foundation
 
 @objc public protocol Authorizer {
-    @objc func fetchAuthValue(socketID: String, channelName: String, completionHandler: (PusherAuth?) -> ())
+    @objc func fetchAuthValue(socketID: String, channelName: String,
+    completionHandler: @escaping (PusherAuth?) -> ())
 }