upgrade to stackdriver exporter v0.12.2 (#575)

Author: rghetia

go.mod

@@ -5,7 +5,7 @@ require (
 	contrib.go.opencensus.io/exporter/jaeger v0.1.1-0.20190430175949-e8b55949d948
 	contrib.go.opencensus.io/exporter/ocagent v0.5.0
 	contrib.go.opencensus.io/exporter/prometheus v0.1.0
-	contrib.go.opencensus.io/exporter/stackdriver v0.12.1
+	contrib.go.opencensus.io/exporter/stackdriver v0.12.2
 	contrib.go.opencensus.io/exporter/zipkin v0.1.1
 	github.com/DataDog/datadog-go v2.2.0+incompatible // indirect
 	github.com/DataDog/opencensus-go-exporter-datadog v0.0.0-20181026070331-e7c4bd17b329

go.sum

@@ -14,6 +14,8 @@ contrib.go.opencensus.io/exporter/prometheus v0.1.0 h1:SByaIoWwNgMdPSgl5sMqM2KDE
 contrib.go.opencensus.io/exporter/prometheus v0.1.0/go.mod h1:cGFniUXGZlKRjzOyuZJ6mgB+PgBcCIa79kEKR8YCW+A=
 contrib.go.opencensus.io/exporter/stackdriver v0.12.1 h1:Dll2uFfOVI3fa8UzsHyP6z0M6fEc9ZTAMo+Y3z282Xg=
 contrib.go.opencensus.io/exporter/stackdriver v0.12.1/go.mod h1:iwB6wGarfphGGe/e5CWqyUk/cLzKnWsOKPVW3no6OTw=
+contrib.go.opencensus.io/exporter/stackdriver v0.12.2 h1:jU1p9F07ASK11wYgSTPKtFlTvTtCDj6R1d3nRt0ZHDE=
+contrib.go.opencensus.io/exporter/stackdriver v0.12.2/go.mod h1:iwB6wGarfphGGe/e5CWqyUk/cLzKnWsOKPVW3no6OTw=
 contrib.go.opencensus.io/exporter/zipkin v0.1.1 h1:PR+1zWqY8ceXs1qDQQIlgXe+sdiwCf0n32bH4+Epk8g=
 contrib.go.opencensus.io/exporter/zipkin v0.1.1/go.mod h1:GMvdSl3eJ2gapOaLKzTKE3qDgUkJ86k9k3yY2eqwkzc=
 contrib.go.opencensus.io/resource v0.1.1/go.mod h1:F361eGI91LCmW1I/Saf+rX0+OFcigGlFvXwEGEnkRLA=