* Update CMakeLists.txt

fix the bug:when build with cmake using option '-DBUILD_SHARED_AND_STATIC_LIBS=ON -DENABLE_CJSON_UTILS=ON', build sucess,
but use cmake comand 'find_package(cjson CONFIG)', 'cjson_utils' target is available,but  'cjson_utils-static' target not exist.