Update copyright

Author: kean

Sources/NaiveDate.swift

@@ -1,6 +1,6 @@
 // The MIT License (MIT)
 //
-// Copyright (c) 2017-2019 Alexander Grebenyuk (github.com/kean).
+// Copyright (c) 2017-2021 Alexander Grebenyuk (github.com/kean).
 
 import Foundation
 

Sources/NaiveDateFormatter.swift

@@ -1,6 +1,6 @@
 // The MIT License (MIT)
 //
-// Copyright (c) 2017-2019 Alexander Grebenyuk (github.com/kean).
+// Copyright (c) 2017-2021 Alexander Grebenyuk (github.com/kean).
 
 import Foundation
 

Tests/NaiveDateFormatterTest.swift

@@ -1,6 +1,6 @@
 // The MIT License (MIT)
 //
-// Copyright (c) 2017-2019 Alexander Grebenyuk (github.com/kean).
+// Copyright (c) 2017-2021 Alexander Grebenyuk (github.com/kean).
 
 import Foundation
 import XCTest

Tests/NaiveDateTests.swift

@@ -1,6 +1,6 @@
 // The MIT License (MIT)
 //
-// Copyright (c) 2017-2019 Alexander Grebenyuk (github.com/kean).
+// Copyright (c) 2017-2021 Alexander Grebenyuk (github.com/kean).
 
 import Foundation
 import XCTest