message: docs: fix italics in custom headers
diff: @@ -474,7 +474,7 @@ Custom request/response headers can be added to a request/response at the weight
  route, virtual host, and/or global route configuration level. See the
  :ref:`v2 <envoy_api_msg_RouteConfiguration>` API documentation.
  -No *:*-prefixed pseudo-header may be modified via this mechanism. The *:path*
  +No *:-prefixed* pseudo-header may be modified via this mechanism. The *:path*
  and *:authority* headers may instead be modified via mechanisms such as
  :ref:`prefix_rewrite <envoy_api_field_route.RouteAction.prefix_rewrite>` and
  :ref:`host_rewrite <envoy_api_field_route.RouteAction.host_rewrite>`.
  