Update Prometheus to 0.9.1 (#2360)

Signed-off-by: Yong Tang <yong.tang.github@outlook.com>

Makefile

@@ -32,7 +32,7 @@ godeps:
 	go get -u github.com/prometheus/client_golang/prometheus
 	(cd $(GOPATH)/src/github.com/mholt/caddy              && git checkout -q v0.11.1)
 	(cd $(GOPATH)/src/github.com/miekg/dns                && git checkout -q v1.1.0)
-	(cd $(GOPATH)/src/github.com/prometheus/client_golang && git checkout -q v0.8.0)
+	(cd $(GOPATH)/src/github.com/prometheus/client_golang && git checkout -q v0.9.1)
 
 .PHONY: travis
 travis:

plugin/metrics/metrics.go

@@ -5,7 +5,6 @@ import (
 	"context"
 	"net"
 	"net/http"
-	"os"
 	"sync"
 	"time"
 
@@ -40,7 +39,7 @@ func New(addr string) *Metrics {
 	}
 	// Add the default collectors
 	met.MustRegister(prometheus.NewGoCollector())
-	met.MustRegister(prometheus.NewProcessCollector(os.Getpid(), ""))
+	met.MustRegister(prometheus.NewProcessCollector(prometheus.ProcessCollectorOpts{}))
 
 	// Add all of our collectors
 	met.MustRegister(buildInfo)