force UTF-8 encoding while parsing CSV file

Depending on the client's locale and the availability on the target system, parsing could fail (see below).
This fix forces the encoding to be always UTF-8, regardless of the client or system default encoding.

perl: warning: Setting locale failed.
perl: warning: Please check that your locale settings:
        LANGUAGE = (unset),
        LC_ALL = (unset),
        LC_CTYPE = "pl_PL.UTF-8",
        LANG = "en_GB.UTF-8"
    are supported and installed on your system.
perl: warning: Falling back to the standard locale ("C").
/home/master/.rvm/rubies/ruby-2.0.0-p247/lib/ruby/2.0.0/csv.rb:1780:in `sub!': invalid byte sequence in US-ASCII (ArgumentError)