Add can build args option

[masakura]

I wan to use File object properties, when invoke spawn,

  gulp.src('book/index.adoc')
    .pipe(spawn({
      cmd: 'asciidoctor-pdf',
      args: file => ['-B', file.base, '-b', 'pdf', '-o-', '-'], // Change base directory to 'book'
      filename: basename => `${basename}.pdf`,
    }))
    .pipe(gulp.dest('dist'));