upgrade golang

Dockerfile

@@ -1,4 +1,4 @@
-FROM --platform=${BUILDPLATFORM:-linux/amd64} golang:1.18-alpine AS build
+FROM --platform=${BUILDPLATFORM:-linux/amd64} golang:1.21-alpine AS build
 ARG TARGETPLATFORM
 ARG BUILDPLATFORM
 ARG VERSION

cmd/main.go

@@ -6,7 +6,6 @@ import (
 	"errors"
 	"flag"
 	"fmt"
-	"io/ioutil"
 	"log"
 	"os"
 	"sort"
@@ -130,7 +129,7 @@ func main() {
 		fileDays := []*ethstore.Day{}
 		_, err := os.Stat(opts.JsonFile)
 		if err == nil {
-			fileDaysBytes, err := ioutil.ReadFile(opts.JsonFile)
+			fileDaysBytes, err := os.ReadFile(opts.JsonFile)
 			if err != nil {
 				log.Fatalf("error reading file: %v", err)
 			}
@@ -163,7 +162,7 @@ func main() {
 			if err != nil {
 				log.Fatalf("error marshaling ethstore: %v", err)
 			}
-			err = ioutil.WriteFile(opts.JsonFile, fileDaysJson, 0644)
+			err = os.WriteFile(opts.JsonFile, fileDaysJson, 0644)
 			if err != nil {
 				log.Fatalf("error writing ethstore to file: %v", err)
 			}

go.mod

@@ -1,6 +1,6 @@
 module github.com/gobitfly/eth.store
 
-go 1.18
+go 1.20
 
 require (
 	github.com/attestantio/go-eth2-client v0.19.9