Update Dockerfile

backend/Dockerfile

@@ -3,7 +3,7 @@ USER root
 RUN apt-get update && apt-get install -y python3-full python3 python3-pip
 COPY requirements.txt .
 RUN python3 -m venv venv
-RUN source venv/bin/activate
+RUN . venv/bin/activate
 RUN python3 -m pip install --no-cache-dir -r requirements.txt
 USER seluser
 WORKDIR /home/seluser