libhext/bindings/python: cmake: use old-style target name on CMake 3.13
libhext/bindings/python: cmake: use old-style target name on CMake 3.13

thomastrapp/hext,thomastrapp/hext,thomastrapp/hext,thomastrapp/hext,thomastrapp/hext,thomastrapp/hext,thomastrapp/hext,thomastrapp/hext