Force strings' encodings to utf-8 to stop an error in dirinfo.rb about encoding

    /home/h2s/.rvm/gems/ruby-2.0.0-p0/gems/greencard-0.0.4/lib/greencard/dirinfo.rb:238:in `join': incompatible character encodings: ASCII-8 BIT and UTF-8 (Encoding::CompatibilityError)
        from /home/h2s/.rvm/gems/ruby-2.0.0-p0/gems/greencard-0.0.4/lib/greencard/dirinfo.rb:238:in `encode'
        from /home/h2s/src/ppl/lib/ppl/adapter/vcard/greencard.rb:26:in `encode'