doc: Update license year range to 2021

COPYING

@@ -1,7 +1,7 @@
 The MIT License (MIT)
 
-Copyright (c) 2009-2020 The Bitcoin Core developers
-Copyright (c) 2009-2020 Bitcoin Developers
+Copyright (c) 2009-2021 The Bitcoin Core developers
+Copyright (c) 2009-2021 Bitcoin Developers
 
 Permission is hereby granted, free of charge, to any person obtaining a copy
 of this software and associated documentation files (the "Software"), to deal

configure.ac

@@ -4,7 +4,7 @@ define(_CLIENT_VERSION_MINOR, 99)
 define(_CLIENT_VERSION_BUILD, 0)
 define(_CLIENT_VERSION_RC, 0)
 define(_CLIENT_VERSION_IS_RELEASE, false)
-define(_COPYRIGHT_YEAR, 2020)
+define(_COPYRIGHT_YEAR, 2021)
 define(_COPYRIGHT_HOLDERS,[The %s developers])
 define(_COPYRIGHT_HOLDERS_SUBSTITUTION,[[Bitcoin Core]])
 AC_INIT([Bitcoin Core],m4_join([.], _CLIENT_VERSION_MAJOR, _CLIENT_VERSION_MINOR, _CLIENT_VERSION_BUILD)m4_if(_CLIENT_VERSION_RC, [0], [], [rc]_CLIENT_VERSION_RC),[https://github.com/bitcoin/bitcoin/issues],[bitcoin],[https://bitcoincore.org/])

contrib/debian/copyright

@@ -5,7 +5,7 @@ Upstream-Contact: Satoshi Nakamoto <satoshin@gmx.com>
 Source: https://github.com/bitcoin/bitcoin
 
 Files: *
-Copyright: 2009-2020, Bitcoin Core Developers
+Copyright: 2009-2021, Bitcoin Core Developers
 License: Expat
 Comment: The Bitcoin Core Developers encompasses the current developers listed on bitcoin.org,
          as well as the numerous contributors to the project.