[PR #1501] Fix filename comment in TaskDelegate header.

The file was likely renamed without the comment being updated. Comment used to report:

```
//  Error.swift
```

Source/TaskDelegate.swift

@@ -1,5 +1,5 @@
 //
-//  Error.swift
+//  TaskDelegate.swift
 //
 //  Copyright (c) 2014-2016 Alamofire Software Foundation (http://alamofire.org/)
 //