fix monitoring.sgml

Author: oneofsunshine

postgresql/doc/src/sgml/monitoring.sgml

@@ -12063,7 +12063,7 @@ ____________________________________________________________________________-->
        The WAL sender process is currently transferring all WAL logs
        generated during the backup. This phase occurs after
        <literal>waiting for wal archiving to finish</literal> phase if
-       <literal>--wal-method=fetch</literal> is specified in
+       <literal>-&minus;wal-method=fetch</literal> is specified in
        <application>pg_basebackup</application>. The backup will end
        when this phase is completed.
       </entry>