[cornerpoint] improve patch for opm-grid

See pull request #327 in opm-grid:
https://github.com/OPM/opm-grid/pull/327

patches/opm-grid-2018.04.patch

+diff --git a/dune.module b/dune.module
+index 9c81972..a711c48 100644
+--- a/dune.module
++++ b/dune.module
+@@ -10,5 +10,5 @@ Label: 2018.04
+ Maintainer: atgeirr@sintef.no
+ MaintainerName: Atgeirr F. Rasmussen
+ Url: http://opm-project.org
+-Depends: dune-common (>= 2.4) dune-geometry (>= 2.4) dune-grid (>= 2.4)
+-Suggests: dune-istl (>= 2.4) opm-common
++Depends: opm-common dune-common (>= 2.4) dune-geometry (>= 2.4) dune-grid (>= 2.4)
++Suggests: dune-istl (>= 2.4)
 diff --git a/opm-grid-prereqs.cmake b/opm-grid-prereqs.cmake
 index 2ad0d86..032ac19 100644
 --- a/opm-grid-prereqs.cmake