refactor: update go version

go.mod

@@ -1,13 +1,14 @@
 module github.com/hanshuaikang/gin-prometheus
 
-go 1.22.4
+go 1.21
 
 require (
 	github.com/gin-gonic/gin v1.10.0
 	github.com/prometheus/client_golang v1.19.1
 	github.com/shirou/gopsutil v3.21.11+incompatible
 	go.opentelemetry.io/otel v1.28.0
 	go.opentelemetry.io/otel/exporters/prometheus v0.50.0
+	go.opentelemetry.io/otel/metric v1.28.0
 	go.opentelemetry.io/otel/sdk v1.28.0
 	go.opentelemetry.io/otel/sdk/metric v1.28.0
 )
@@ -45,7 +46,6 @@ require (
 	github.com/twitchyliquid64/golang-asm v0.15.1 // indirect
 	github.com/ugorji/go/codec v1.2.12 // indirect
 	github.com/yusufpapurcu/wmi v1.2.4 // indirect
-	go.opentelemetry.io/otel/metric v1.28.0 // indirect
 	go.opentelemetry.io/otel/trace v1.28.0 // indirect
 	golang.org/x/arch v0.8.0 // indirect
 	golang.org/x/crypto v0.24.0 // indirect