bug#14545: date --iso-8601 should use colon in time zone offset

[Assaf Gordon]

tags 14545 fixed
close 14545
stop

(triaging old bugs)

This was fixed in:
https://git.savannah.gnu.org/cgit/coreutils.git/commit/?id=17bbf6ce44eb543a95695fa9d2cbd70fb52c6f42

Marking as "fixed" and closing.

-assaf