Docstring for bucket.setMetadata has invalid argument

[dhermes]

From the code:

bucket.setMetadata({
  contentType: 'application/x-font-ttf',
  metadata: {
    my: 'custom',
    properties: 'go here'
  }
}, function(err, metadata) {});

[ryanseys]

You're very right. In fact, I don't think buckets have arbitrary metadata field you can set on them so all of those are incorrect. I've created #371 in order to hopefully clear this up. Let me know what you think.