[!316] bump the required version of dune-uggrid to 2.7

Merge branch 'fix/bump-required-version-of-uggrid' into 'master'

See merge request [!316]

  [!316]: gitlab.dune-project.org/core/dune-grid/merge_requests/316

dune.module

@@ -2,5 +2,5 @@ Module: dune-grid
 Version: 2.7-git
 Maintainer: dune-devel@lists.dune-project.org
 Depends: dune-geometry (>= 2.6)
-Suggests: dune-uggrid (>=2.6)
+Suggests: dune-uggrid (>=2.7)
 Whitespace-Hook: Yes