Bugfix for creating root spans through plugin API (#389)
Bugfix for creating root spans through plugin API (#389)

PR-URL: #389 
googleapis/cloud-trace-nodejs,matthewloring/cloud-trace-nodejs,matthewloring/cloud-trace-nodejs,keymetrics/vxx,keymetrics/trassingue,matthewloring/cloud-trace-nodejs,googleapis/cloud-trace-nodejs,keymetrics/vxx,googleapis/cloud-trace-nodejs,keymetrics/trassingue,googleapis/cloud-trace-nodejs