add CMAKE_CXX_STANDARD 14 for make_unique

[kintzhao]

~/code_fusion_ws/src/imu_x_fusion/src/imu_vo_ekf.cpp:41:21: error: ‘make_unique’ is not a member of ‘std’ ekfptr = std::make_unique(acc_n, gyr_n, acc_w, gyr_w);