Code cleaning (remove python2)

cps/services/worker.py

@@ -1,5 +1,21 @@
+# -*- coding: utf-8 -*-
+
+#  This file is part of the Calibre-Web (https://github.com/janeczku/calibre-web)
+#    Copyright (C) 2020 pwr
+#
+#  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
+#  the Free Software Foundation, either version 3 of the License, or
+#  (at your option) any later version.
+#
+#  This program is distributed in the hope that it will be useful,
+#  but WITHOUT ANY WARRANTY; without even the implied warranty of
+#  MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE.  See the
+#  GNU General Public License for more details.
+#
+#  You should have received a copy of the GNU General Public License
+#  along with this program. If not, see <http://www.gnu.org/licenses/>.
 
-from __future__ import division, print_function, unicode_literals
 import threading
 import abc
 import uuid