[version] Bump up version to 3.4-git

dune.module

 Module: dumux
-Version: 3.3-git
+Version: 3.4-git
 Maintainer: dumux@listserv.uni-stuttgart.de
 Depends: dune-common (>= 2.7) dune-grid (>= 2.7) dune-localfunctions (>= 2.7) dune-istl (>= 2.7)
 Suggests: dune-alugrid (>=2.7) dune-foamgrid (>=2.7) dune-uggrid (>=2.7) dune-functions (>=2.7) opm-common opm-grid dune-subgrid dune-spgrid (>= 2.7) dune-mmesh (>= 1.1)