William Pitcock 28578c6ab5 activitypub: fix date header format
HTTP date header specification says that days must always be two-digit.
Accordingly, change the format string used to ensure days are always
represented as two-digit (e.g. 01).
2019-03-01 22:32:00 +03:00
..
2018-03-30 15:01:53 +02:00
2018-03-30 15:01:53 +02:00
2018-03-30 15:01:53 +02:00