refactor: move from io/ioutil to io and os package (#2236)

The io/ioutil package has been deprecated as of Go 1.16, see
https://golang.org/doc/go1.16#ioutil. This commit replaces the existing
io/ioutil functions with their new definitions in io and os packages.

Signed-off-by: Eng Zer Jun <engzerjun@gmail.com>

pkg/fission-cli/cmd/spec/validate.go

@@ -19,7 +19,6 @@ package spec
 import (
 	"bytes"
 	"fmt"
-	"io/ioutil"
 	"os"
 	"path/filepath"
 	"strings"
@@ -234,7 +233,7 @@ func ReadSpecs(specDir string) (*FissionResources, error) {
 			return nil
 		}
 		// read
-		b, err := ioutil.ReadFile(path)
+		b, err := os.ReadFile(path)
 		if err != nil {
 			result = multierror.Append(result, err)
 			return nil