Update copyright dates.

Author: tkremenek

README.md

@@ -117,7 +117,7 @@ The Swift package manager uses [llbuild](https://github.com/apple/swift-llbuild)
 
 ## License
 
-Copyright 2015 - 2019 Apple Inc. and the Swift project authors. Licensed under Apache License v2.0 with Runtime Library Exception.
+Copyright 2015 - 2020 Apple Inc. and the Swift project authors. Licensed under Apache License v2.0 with Runtime Library Exception.
 
 See [https://swift.org/LICENSE.txt](https://swift.org/LICENSE.txt) for license information.