[bugfix] Fix wrong named argument in dune_register_package_flags usage

The Metis test used the wrong one and I copied it for PTScotch... :/

cmake/modules/FindMETIS.cmake

@@ -94,5 +94,5 @@ endif(METIS_FOUND)
 # register all METIS related flags
 if(METIS_FOUND)
   dune_register_package_flags(LIBRARIES "${METIS_LIBRARIES}"
-                              INCLUDE_DIRECTORIES "${METIS_INCLUDE_DIRS}")
+                              INCLUDE_DIRS "${METIS_INCLUDE_DIRS}")
 endif()

cmake/modules/FindPTScotch.cmake

@@ -75,7 +75,7 @@ if(PTSCOTCH_FOUND)
     "Library directory: ${PTSCOTCH_LIBRARIES}\n\n")
 
   dune_register_package_flags(LIBRARIES "${PTSCOTCH_LIBRARIES}"
-                              INCLUDE_DIRECTORIES "${PTSCOTCH_INCLUDE_DIRS}")
+                              INCLUDE_DIRS "${PTSCOTCH_INCLUDE_DIRS}")
 endif(PTSCOTCH_FOUND)
 
 mark_as_advanced(PTSCOTCH_INCLUDE_DIR PTSCOTCH_LIBRARIES HAVE_PTSCOTCH)