make it go1.14 buildable

Author: mlusetti

handlers.go

@@ -2,9 +2,9 @@ package restserver
 
 import (
 	"errors"
-	"io/fs"
 	"log"
 	"net/http"
+	"os"
 	"path"
 	"path/filepath"
 	"strings"
@@ -93,8 +93,8 @@ func (s *Server) ServeHTTP(w http.ResponseWriter, r *http.Request) {
 		QuotaManager:   s.quotaManager, // may be nil
 		PanicOnError:   s.PanicOnError,
 		NoVerifyUpload: s.NoVerifyUpload,
-		DirMode:        fs.FileMode(s.DirMode),
-		FileMode:       fs.FileMode(s.FileMode),
+		DirMode:        os.FileMode(s.DirMode),
+		FileMode:       os.FileMode(s.FileMode),
 	}
 	if s.Prometheus {
 		opt.BlobMetricFunc = makeBlobMetricFunc(username, folderPath)