Specify POD character encoding (UTF-8)

This fixes a test failure of Test::Pod, at least on Perl 5.18 (Test::Pod 1.48):

    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