science/dynare: Correct the command recommended in pkg-message

The --persist argument is needed on FreeBSD, otherwise the
command SEGVs. But on Ubuntu this argument isn't needed.
The reason, perhaps, is that Octave's graphical backend there
is gnome, and on FreeBSD graphical backend is qt.

science/dynare/files/pkg-message.in

@@ -14,7 +14,7 @@ or
    session.
 
 You can also run Dynare using one command:
-$ octave --eval 'dynare {example}.mod {args}'
+$ octave --eval 'dynare {example}.mod {args}' --persist
 
 EOM
 }