Allow also ranges of years when testing.

Yet we only allowed expressions like '2012, 2014' etc. when telling
which year a copyright was assigned at. Now we also allow ranges like
'2012-2014'.

tests/test_diceware.py

@@ -261,7 +261,7 @@ class TestDicewareModule(object):
     def test_print_version_current_year(self, capsys):
         # in version infos we display the current year
         print_version()
-        pattern = ".*\(C\) (20[0-9]{2}, )*%s.*" % (
+        pattern = ".*\(C\) (20[0-9]{2}([,\-] ?))*%s.*" % (
             datetime.datetime.now().year)
         out, err = capsys.readouterr()
         assert re.match(pattern, out, re.M + re.S) is not None