Fix shell command in Dockerfile

Dockerfile

@@ -34,12 +34,13 @@ WORKDIR /app
 COPY requirements.txt .
 
 RUN python3 -m venv /opt/mineru_venv && \
-    source /opt/mineru_venv/bin/activate && \
+    . /opt/mineru_venv/bin/activate && \
     pip install --upgrade pip && \
     pip install -r requirements.txt
 
 # Download model + setup config
 RUN wget https://github.com/opendatalab/MinerU/raw/master/scripts/download_models_hf.py -O download_models.py && \
+    . /opt/mineru_venv/bin/activate && \
     python3 download_models.py && \
     wget https://github.com/opendatalab/MinerU/raw/master/magic-pdf.template.json -O /root/magic-pdf.json && \
     sed -i 's|"device": "cpu"|"device": "cpu"|g' /root/magic-pdf.json