Docs: updated unitd.8 date.

We've applied significant changes to the page, so let's update the date.
While we're at it, let's change it to use ISO 8601 format for the date.

Reviewed-by: Artem Konev <[email protected]>
Signed-off-by: Alejandro Colomar <[email protected]>

Author: alejandro-colomar

docs/man/man8/unitd.8.in

@@ -1,6 +1,6 @@
 .\" (C) 2017-2021, NGINX, Inc.
 .\"
-.Dd March 16, 2021
+.Dd 2023-04-26
 .Dt unitd 8
 .Os NGINX Unit
 .Sh Name