mysql/mariadb应该使用utf8mb4而不是utf8

详情参考https://mp.weixin.qq.com/s?__biz=MzIwMzg1ODcwMw==&mid=2247487968&idx=1&sn=2ff7b511f6727c7816ab02fc0e1c0361&chksm=96c9a780a1be2e961cd5e7c5e5ff32961cd2b6c1bac480f8f1c3f281e5bf1504fecebdd59d48#rd