Update year in docs and main copyright file.

COPYRIGHT

 diceware -- Python implementation
-Copyright (C) 2015-2017 Uli Fouquet and contributors
+Copyright (C) 2015-2018 Uli Fouquet and contributors
 
 This program is free software: you can redistribute it and/or modify
 it under the terms of the GNU General Public License as published by

docs/conf.py

@@ -53,7 +53,7 @@ master_doc = 'index'
 
 # General information about the project.
 project = 'diceware'
-copyright = '2015-2017, Uli Fouquet'
+copyright = '2015-2018, Uli Fouquet'
 
 # The version info for the project you're documenting, acts as replacement for
 # |version| and |release|, also used in various other places throughout the