code: function execWithSpawn (argv, cwd, cb) {
    cwd = cwd || process.cwd()
    var opts = [
      '-Dplantuml.include.path=' + cwd,
      '-Djava.awt.headless=true',
      '-jar', PLANTUML_JAR
    ].concat(argv)
    return childProcess.spawn('java', opts)
  }
docs: TODO: proper error handling