Reference the open RFC 3339 standard instead of ISO 8601. Firstly,
because closed standards are not something people can easily look into. Secondly, because we only need a very small subset of what ISO 8601
defines and RFC 3339 provides exactly that.

Signed-off-by: Michał Górny <mgorny@gentoo.org>
---
glep-0074.rst | 12 ++++++++----
1 file changed, 8 insertions(+), 4 deletions(-)

diff --git a/glep-0074.rst b/glep-0074.rst
index d5e5057..71167c7 100644
--- a/glep-0074.rst
+++ b/glep-0074.rst
@@ -8,8 +8,9 @@ Type: Standards Track
Status: Final
Version: 1.3
Created: 2017-10-21
-Last-Modified: 2022-10-04
-Post-History: 2017-10-26, 2017-11-16, 2018-02-08, 2022-09-08, 2022-09-11 +Last-Modified: 2022-10-22
+Post-History: 2017-10-26, 2017-11-16, 2018-02-08, 2022-09-08, 2022-09-11,
+ 2022-10-22
Content-Type: text/x-rst
Requires: 59, 61
Replaces: 44, 58, 60
@@ -267,8 +268,8 @@ The Manifest files can specify the following tags:

``TIMESTAMP <iso8601>``
Specifies a timestamp of when the Manifest file was last updated.
- The timestamp must be a valid second-precision ISO 8601 extended
- format combined date and time in UTC timezone, i.e. using
+ The timestamp must be a valid second-precision RFC 3339 format
+ combined date and time in UTC timezone [#RFC3339]_