argv.filters can be an array if there is multiple options :

    --filters foo # => [ 'foo' ]
    --filters a --filters b --filters c # => [ 'a', 'b', 'c' ]

By using `[].concat(argv.filters)` we ensure that it will always be an array, then we join all part with a comma and split it in order to keep backward compatibility with the previous syntax (`--filters foo,bar --filters a,b,c` will be `[ 'foo', 'bar', 'a', 'b', 'c' ]`).