ci: use deb mirror from ustc

.drone.yml

@@ -27,8 +27,8 @@ steps:
         from_secret: NETLIFY_API_KEY
     commands:
       #   - git config --global --add safe.directory "/drone/src"
-      # 让 Debian 使用网易源。阿里的源有限速。
-      - sed -i 's/deb.debian.org/mirrors.163.com/g' /etc/apt/sources.list
+      # 让 Debian 使用中科大源；测试网易和阿里的源速度不理想。
+      - sed -i 's/deb.debian.org/mirrors.ustc.edu.cn/g' /etc/apt/sources.list
       - apt-get update && apt-get install -y zip jq tar gzip curl
       - (cd dist && zip -r -9 ../um-react.zip .)
       - ./scripts/publish.sh