fixed parameter markup

Author: mumumu

appendices/migration85/incompatible.xml

@@ -391,7 +391,8 @@
 
   <para>
    <methodname>SoapClient::__doRequest</methodname> now accepts a new,
-   optional $uriParserClass parameter accepting string or null arguments.
+   optional <parameter>$uriParserClass</parameter> parameter accepting
+   string or null arguments.
    Null represents the original (<function>parse_url</function>) based
    method, while the new backends will be used when passing either
    Uri\Rfc3986\Uri::class or Uri\WhatWg\Url::class.