Merge #2061: [Trivial] Add Zcash copyright statement

4fcbc39 Trivial: Add Zcash copyright (random-zebra)

Pull request description:

  Add `The Zcash developers` to the `COPYING` file.

ACKs for top commit:
  furszy:
    utACK 4fcbc39
  Fuzzbawls:
    ACK 4fcbc39

Tree-SHA512: 01943b46d780662e1fab4e3b3300867bffd5381e4bba1aa067d1e52eee1cac6bb0d872513411b24be7f15b45f5840182917ae43b236a9d048462877b3f0f36f6

COPYING

@@ -3,6 +3,7 @@ Copyright (c) 2014-2015 Dash Developers
 Copyright (c) 2011-2013 The PPCoin developers
 Copyright (c) 2013-2014 The NovaCoin Developers
 Copyright (c) 2014-2018 The BlackCoin Developers
+Copyright (c) 2016-2020 The Zcash developers
 Copyright (c) 2015-2020 PIVX Developers
 
 Permission is hereby granted, free of charge, to any person obtaining a copy