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/router/functionHandler.go

@@ -21,7 +21,6 @@ import (
 	"context"
 	"fmt"
 	"io"
-	"io/ioutil"
 	"math/rand"
 	"net"
 	"net/http"
@@ -242,7 +241,7 @@ func (roundTripper *RetryingRoundTripper) RoundTrip(req *http.Request) (*http.Re
 						Proto:         req.Proto,
 						ProtoMajor:    req.ProtoMajor,
 						ProtoMinor:    req.ProtoMinor,
-						Body:          ioutil.NopCloser(bytes.NewBufferString(errMsg)),
+						Body:          io.NopCloser(bytes.NewBufferString(errMsg)),
 						ContentLength: int64(len(errMsg)),
 						Request:       req,
 						Header:        make(http.Header),