[v9_11] change markdown comment style for pandoc

doc/dev/dev.md

@@ -1,10 +1,10 @@
-<!---
+<!--
  - Copyright (C) 2017  Internet Systems Consortium, Inc. ("ISC")
  -
  - This Source Code Form is subject to the terms of the Mozilla Public
  - License, v. 2.0. If a copy of the MPL was not distributed with this
  - file, You can obtain one at http://mozilla.org/MPL/2.0/.
---->
+-->
 ## BIND Developer Information
 
 ### Contents