Bump Go version in go.mod and fix staticcheck errors

gen/main.go

@@ -4,7 +4,6 @@ package main
 
 import (
 	"fmt"
-	"io/ioutil"
 	"log"
 	"os"
 	"path"
@@ -30,7 +29,7 @@ func main() {
 	// directory.
 	//
 	// The custom bindings are named with a "a__" prefix. Keep those.
-	fis, err := ioutil.ReadDir(dstDir)
+	fis, err := os.ReadDir(dstDir)
 	if err != nil {
 		log.Fatal(err)
 	}
@@ -61,7 +60,7 @@ func main() {
 			filename = strings.TrimPrefix(filename, "/")
 			target := filepath.Join(dstDir, fi.Name())
 
-			if err := ioutil.WriteFile(target, []byte(fmt.Sprintf(`#ifndef LIBWEBP_NO_SRC
+			if err := os.WriteFile(target, []byte(fmt.Sprintf(`#ifndef LIBWEBP_NO_SRC
 #include "../../libwebp_src/%s"
 #endif
 `, filename)), 0o644); err != nil {
@@ -70,7 +69,6 @@ func main() {
 
 			return nil
 		})
-
 		if err != nil {
 			log.Fatal(err)
 		}

go.mod

@@ -1,5 +1,5 @@
 module github.com/bep/gowebp
 
-go 1.16
+go 1.20
 
 require golang.org/x/image v0.0.0-20210220032944-ac19c3e999fb // indirect

libwebp/encode_test.go

@@ -6,10 +6,7 @@ import (
 	"image"
 	"image/draw"
 	"image/jpeg"
-	_ "image/jpeg"
-	_ "image/png"
 	"io"
-	"io/ioutil"
 	"os"
 	"path/filepath"
 	"runtime"
@@ -108,7 +105,7 @@ func TestEncodeLongRunning(t *testing.T) {
 				t.Fatal(err)
 			}
 
-			if err = Encode(ioutil.Discard, img, test.opts); err != nil {
+			if err = Encode(io.Discard, img, test.opts); err != nil {
 				t.Fatal(err)
 			}
 		}
@@ -138,7 +135,7 @@ func BenchmarkEncode(b *testing.B) {
 
 			b.ResetTimer()
 			for i := 0; i < b.N; i++ {
-				if err = Encode(ioutil.Discard, imgrgba, test.opts); err != nil {
+				if err = Encode(io.Discard, imgrgba, test.opts); err != nil {
 					b.Fatal(err)
 				}
 			}
@@ -163,7 +160,7 @@ func BenchmarkEncodeJpeg(b *testing.B) {
 	}
 
 	for i := 0; i < b.N; i++ {
-		if err = jpeg.Encode(ioutil.Discard, img, opts); err != nil {
+		if err = jpeg.Encode(io.Discard, img, opts); err != nil {
 			b.Fatal(err)
 		}
 	}