refactor(plugins): replace deprecated io/ioutil functions

The io/ioutil package has been deprecated as of Go 1.16 [1]. This commit
replaces the existing io/ioutil functions with their new definitions in
io and os packages.

[1]: https://golang.org/doc/go1.16#ioutil
Signed-off-by: Eng Zer Jun <engzerjun@gmail.com>

plugins/builder/functions.go

@@ -3,7 +3,6 @@ package builder
 import (
 	"bytes"
 	"errors"
-	"io/ioutil"
 	"os"
 	"path"
 	"strings"
@@ -35,7 +34,7 @@ func listImagesByImageRepo(imageRepo string) ([]string, error) {
 }
 
 func removeAllContents(basePath string) error {
-	dir, err := ioutil.ReadDir(basePath)
+	dir, err := os.ReadDir(basePath)
 	if err != nil {
 		return err
 	}

plugins/builder/triggers.go

@@ -3,7 +3,6 @@ package builder
 import (
 	"errors"
 	"fmt"
-	"io/ioutil"
 	"os"
 	"path/filepath"
 	"strings"
@@ -71,7 +70,7 @@ func TriggerCorePostExtract(appName string, sourceWorkDir string) error {
 		return fmt.Errorf("Specified build-dir not found in sourcecode working directory: %v", buildDir)
 	}
 
-	tmpWorkDir, err := ioutil.TempDir(os.TempDir(), fmt.Sprintf("dokku-%s-%s", common.MustGetEnv("DOKKU_PID"), "CorePostExtract"))
+	tmpWorkDir, err := os.MkdirTemp(os.TempDir(), fmt.Sprintf("dokku-%s-%s", common.MustGetEnv("DOKKU_PID"), "CorePostExtract"))
 	if err != nil {
 		return fmt.Errorf("Unable to create temporary working directory: %v", err.Error())
 	}