all: replace io/ioutil with io and os package

Change-Id: I3c6860d1758ac49b13fbb545e1e1957e345153ae
GitHub-Last-Rev: 9f43b2bf417cfdfe750b48cccd429cd1aded809c
GitHub-Pull-Request: golang/vulndb#997
Reviewed-on: https://go-review.googlesource.com/c/vulndb/+/430855
TryBot-Result: Gopher Robot <gobot@golang.org>
Reviewed-by: Dmitri Shuralyov <dmitshur@google.com>
Reviewed-by: Damien Neil <dneil@google.com>
Run-TryBot: Damien Neil <dneil@google.com>
diff --git a/all_test.go b/all_test.go
index 142512e..33bf037 100644
--- a/all_test.go
+++ b/all_test.go
@@ -9,7 +9,6 @@
 
 import (
 	"errors"
-	"io/ioutil"
 	"os"
 	"os/exec"
 	"path/filepath"
@@ -50,7 +49,7 @@
 	allFiles := make(map[string]string)
 	var reports []string
 	for _, dir := range []string{reportsDir, excludedDir} {
-		files, err := ioutil.ReadDir(dir)
+		files, err := os.ReadDir(dir)
 		if err != nil && !errors.Is(err, os.ErrNotExist) {
 			t.Fatalf("unable to read %v/: %s", dir, err)
 		}