Explicitly specify the input file encoding as utf-8

Hello,

`ante.rb` does not work when `LANG=C`.

````
$ LANG=C ruby -v ante.rb hello.ante
ruby 2.1.2p95 (2014-05-08 revision 45877) [x86_64-linux]
ante.rb:46:in `split': invalid byte sequence in US-ASCII (ArgumentError)
        from ante.rb:46:in `parse'
        from ante.rb:29:in `run'
        from ante.rb:162:in `<main>'
````

This can be fixed by specifying the input file encoding explicitly.

Thank you,