Merge branch 'fix/cmake-example-shallowwater' into 'master'

[examples] Fix CMake warning about missing named argument

See merge request !1788

examples/shallowwaterfriction/CMakeLists.txt

-add_input_file_links()
-dune_symlink_to_source_files("params.input")
-
+dune_symlink_to_source_files(FILES "params.input")
 
 dune_add_test(NAME example_shallowwaterfriction
               SOURCES main.cc