Update copyright year

Author: MaxDesiatov

lib/Driver/WebAssemblyToolChains.cpp

@@ -2,7 +2,7 @@
 //
 // This source file is part of the Swift.org open source project
 //
-// Copyright (c) 2014 - 2018 Apple Inc. and the Swift project authors
+// Copyright (c) 2014 - 2021 Apple Inc. and the Swift project authors
 // Licensed under Apache License v2.0 with Runtime Library Exception
 //
 // See https://swift.org/LICENSE.txt for license information