feat: update docker file

backend/Dockerfile

@@ -4,9 +4,8 @@ FROM docker.hub.ipao.vip/jrottenberg/ffmpeg:4.4-alpine
 RUN apk add --no-cache tzdata && \
     cp /usr/share/zoneinfo/Asia/Shanghai /etc/localtime && \
     echo "Asia/Shanghai" > /etc/timezone && \
-    apk del tzdata
-
-RUN mkdir /app/downloads /app/dist
+    apk del tzdata && \
+    mkdir -p /app/downloads /app/dist
 
 COPY backend/build/app /app/app
 COPY backend/config.prod.toml /app/config.toml