message: Docs: Fix header
diff: @@ -166,7 +166,7 @@ following features are available:
  .. _config_http_conn_man_headers_x-ot-span-context:
  x-ot-span-context
  -_________________
  +-----------------
  The *x-ot-span-context* HTTP header is used by Envoy to establish proper parent-child relationships
  between tracing spans for LightStep tracing. *x-ot-span-context* is a Base64 encoded
  