pubsub: publisher().publish() returns an array when used with promises

[kevynb]

Hello,

I use the lib with promises instead of callbacks and when I publish a message I expect to get the messageId as a string, however I get an array containing the string: ['some-id']. Since the documentation seems to say otherwise, I assume it's a bug

It works correctly when I use it with a callback.

Environment details

• OS: MacOS
• Node.js version: 8.5
• google-cloud-node version: 0.14.5

Steps to reproduce

1. require google-cloud

    const buffer = new Buffer(JSON.stringify(message));
    const r = await this.pubsub.topic(topicName).publisher().publish(buffer)[0];
    console.log('messageId', r);

Thanks!