simplify interop-mongo-express (#401)
simplify interop-mongo-express (#401)

PR-URL: https://github.com/GoogleCloudPlatform/cloud-trace-nodejs/pull/401
keymetrics/trassingue,googleapis/cloud-trace-nodejs,keymetrics/trassingue,matthewloring/cloud-trace-nodejs,googleapis/cloud-trace-nodejs,googleapis/cloud-trace-nodejs,keymetrics/vxx,googleapis/cloud-trace-nodejs,matthewloring/cloud-trace-nodejs,keymetrics/vxx,matthewloring/cloud-trace-nodejs