Update Dockerfile

Dockerfile

@@ -8,7 +8,8 @@ RUN apt-get update && \
     apt-get install git python3-pip -y && \
     git clone https://github.com/Paraworks/BangDreamAi /app --depth=1 -b light && \
     cd /app && \
-    pip install --no-cache-dir -r requirements.txt
+    pip install --no-cache-dir -r requirements.txt && \
+    pip install gunicorn==21.2.0
 
 # 开放默认端口
 EXPOSE 7860