Johan Wikman ec08f1b276 Add script for updating Change Date
Running

    $ script/update-change-date 2019-01-01 2019-07-01

will update the Change Date in a file from 2019-01-01 to 2019-07-01,
provided the change date looks exactly like

    Change Date: YYYY-MM-DD
2016-08-17 11:02:43 +03:00
..
2016-08-17 10:06:35 +03:00