fix a formatting typo in protocol docs

docs/source/protocol.rst

@@ -7,11 +7,11 @@ This module implements a Flask-based webservice which
 communicates with clients over HTTP.
 Responses to valid requests are returned as JSON messages.
 The server will therefore return an error unless
-`application/json` is in the `Accept` request header field.
+``application/json`` is in the ``Accept`` request header field.
 
 HTTP communication and JSON grammar details are
 beyond the scope of this document.
-Please refer to [RFC 2616](https://tools.ietf.org/html/rfc2616)
+Please refer to `RFC 2616 <https://tools.ietf.org/html/rfc2616>`_
 and www.json.org for more details.
 
 .. contents:: :local: