[!145] [cmake] Require CMake 3.13

Merge branch 'feature/require-cmake-3.13' into 'master'

See merge request [!145]

  [!145]: Nonecore/dune-geometry/merge_requests/145

CMakeLists.txt

@@ -2,7 +2,7 @@
 project("dune-geometry" C CXX)
 
 # general stuff
-cmake_minimum_required(VERSION 3.1)
+cmake_minimum_required(VERSION 3.13)
 
 if(NOT (dune-common_DIR OR dune-common_ROOT OR
         "${CMAKE_PREFIX_PATH}" MATCHES ".*dune-common.*"))