fix time update in travis

.travis.yml

@@ -6,7 +6,7 @@ go_import_path: v2ray.com/core
 git:
   depth: 5
 before_script:
-- sudo ntpdate time.google.com
+- sudo ntpdate -u time.google.com
 - date
 script:
 - go test -tags json -v v2ray.com/core/...