Specify POD character encoding (UTF-8)

This fixes a test failure of Test::Pod, at least on Perl 5.18:

 t/pod.t ........... 1/7
 #   Failed test 'POD test for blib/lib/WWW/YoutubeViewer.pm'
 #   at /usr/share/perl5/Test/Pod.pm line 186.
 Wide character in print at /usr/share/perl/5.18/Test/Builder.pm line 1759.
 # blib/lib/WWW/YoutubeViewer.pm (1981): Non-ASCII character seen before =encoding in 'Șuteu,'. Assuming UTF-8
Merge pull request #47 from olof/topic/pod_test_fail_utf8

Specify POD character encoding (UTF-8)