Bug 8251 - Follow up, use 'day' instead of 'days' for Datetime::truncate

Bug 8251 - Follow up, use 'day' instead of 'days' for Datetime::truncate

As noted in comment #4 by Jonathan Druart, this should be fixed in every call
to DateTie::truncate function. This patch does exactly that.

julian_m tested that truncate( to => 'days' ) didn't actually do anything, so
it is understandable that this 'fix' might introduce new bugs as we might have
'fixed' at a higher libs level this issue.

'minutes' is used in truncate function too, so fixing.

Signed-off-by: Dobrica Pavlinusic <dpavlin@rot13.org>
Signed-off-by: Paul Poulain <paul.poulain@biblibre.com>