[Fix] Update mailing lists addresses.

dune.module

 Module: dune-grid
 Version: 2.6-git
-Maintainer: dune-devel@dune-project.org
+Maintainer: dune-devel@lists.dune-project.org
 Depends: dune-geometry (>= 2.6)
 Suggests: dune-uggrid
 Whitespace-Hook: Yes

dune/grid/uggrid.hh

@@ -222,7 +222,7 @@ namespace Dune {
      to learn how to create UGGrid objects.
 
      Please send any questions, suggestions, or bug reports to the Dune mailing list
-     dune@dune-project.org
+     dune@lists.dune-project.org
 
      For installation instructions see http://www.dune-project.org/external_libraries/install_ug.html .
    */