Support methods that return a Promise

[kdiogenes]

Hey,

I'm not much versed in JavaScript, but I think that this can be a good solution:

#{source}

try {
  const args = #{args}
  Promise.resolve(#{func}(...args)).then(result => {
    const output = JSON.stringify(['ok', result, []])
    process.stdout.write(output)
  })
} catch (err) {
  process.stdout.write(JSON.stringify(['err', '' + err, err.stack]))
}

I will write a PR with it, just would like to open the discussion.

Best regards!

[kdiogenes]

Just created a PR: https://github.com/bridgetownrb/node-runner/pull/3

[jaredcwhite]

Thanks @kdiogenes!