change =encoding utf8 to =encoding UTF-8 in Loader

change =encoding utf8 to =encoding UTF-8 in Loader

I didn't know why 02pod.t was erroneously passing for me, ilmari pointed
out that my Pod::Simple was out of date, and I needed at least 3.21.

Upgrading Pod::Simple caused 02pod.t to produce the fail when the
=encoding directive was missing.

I like using the UTF-8 encoding rather than the more lax utf8 encoding,
so change it now that I can properly test it out.