Revert "RFC1123 is wrong protocol format for AWS"

This reverts commit c7b1f8ded8.

pkg/api/minioapi/headers.go

@@ -22,6 +22,7 @@ import (
 	"encoding/xml"
 	"net/http"
 	"strconv"
+	"time"
 
 	mstorage "github.com/minio-io/minio/pkg/storage"
 )
@@ -55,13 +56,9 @@ func writeErrorResponse(w http.ResponseWriter, response interface{}, acceptsType
 	return bytesBuffer.Bytes()
 }
 
-const (
-	sendFormat = "2006-01-02T15:04:05.000Z"
-)
-
 // Write object header
 func writeObjectHeaders(w http.ResponseWriter, metadata mstorage.ObjectMetadata) {
-	lastModified := metadata.Created.Format(sendFormat)
+	lastModified := metadata.Created.Format(time.RFC1123)
 	// common headers
 	writeCommonHeaders(w, metadata.ContentType)
 	w.Header().Set("ETag", metadata.ETag)