New Biber prerequisites

[Ken Brown]

Hi Achim,

The next Biber release will have a few new prerequisites:
perl-DateTime-Calendar-Julian
perl-DateTime-Format-Builder
perl-PerlIO-utf8_strict
perl-Sort-Key

Please add them when you get a chance.  This won't be relevant until 
you're ready to update Perl to 5.26, so there's no rush.

Thanks.

Ken