lint by golangci-lint (#3080)

pkg/metrics/aggregate/server.go

@@ -30,7 +30,7 @@ func EnablePrometheus() {
 	sm.Add(prometheus.ServerMetrics)
 }
 
-var sm *serverMetrics = &serverMetrics{}
+var sm = &serverMetrics{}
 
 func init() {
 	metrics.Register(sm)

pkg/metrics/mem/server.go

@@ -23,9 +23,12 @@ import (
 	server "github.com/fatedier/frp/server/metrics"
 )
 
-var sm *serverMetrics = newServerMetrics()
-var ServerMetrics server.ServerMetrics
-var StatsCollector Collector
+var (
+	sm = newServerMetrics()
+
+	ServerMetrics  server.ServerMetrics
+	StatsCollector Collector
+)
 
 func init() {
 	ServerMetrics = sm

pkg/metrics/metrics.go

@@ -4,5 +4,7 @@ import (
 	"github.com/fatedier/frp/pkg/metrics/aggregate"
 )
 
-var EnableMem = aggregate.EnableMem
-var EnablePrometheus = aggregate.EnablePrometheus
+var (
+	EnableMem        = aggregate.EnableMem
+	EnablePrometheus = aggregate.EnablePrometheus
+)

pkg/metrics/prometheus/server.go

@@ -1,9 +1,9 @@
 package prometheus
 
 import (
-	"github.com/fatedier/frp/server/metrics"
-
 	"github.com/prometheus/client_golang/prometheus"
+
+	"github.com/fatedier/frp/server/metrics"
 )
 
 const (