Add =encoding utf8 to the 5.12 delta (like the 5.10 delta)

Add =encoding utf8 to the 5.12 delta (like the 5.10 delta)

Without specifying =encoding POD converters would produce strings like
"Ævar" from the source "Ævar". This affected the Acknowledgements
section where several non-ASCII names were present.

Tested by checking if search.cpan.org screwed up non-ASCII characters
in the 5.10 delta, it didn't.