http: return response object for chaining #481 (#482)
http: return response object for chaining #481 (#482)

PR-URL: https://github.com/GoogleCloudPlatform/cloud-trace-nodejs/pull/482
matthewloring/cloud-trace-nodejs,keymetrics/trassingue,googleapis/cloud-trace-nodejs,keymetrics/trassingue,googleapis/cloud-trace-nodejs,keymetrics/vxx,keymetrics/vxx,matthewloring/cloud-trace-nodejs,googleapis/cloud-trace-nodejs,matthewloring/cloud-trace-nodejs,googleapis/cloud-trace-nodejs