fix: dockerfiles

docker/python-3.6-gpu.dockerfile

@@ -45,11 +45,13 @@ RUN apt-get update \
     && apt-mark hold libcudnn7 \
     && rm -rf /var/lib/apt/lists/*
 
+RUN mkdir -p /model
+ENV MODEL_PATH /model
+COPY audio_example.mp3 .
 
 # Spleeter installation.
 RUN apt-get update && apt-get install -y ffmpeg libsndfile1
 RUN pip install musdb museval
 RUN pip install spleeter-gpu==1.4.5
-RUN mkdir -p /model
-ENV MODEL_PATH /model
+
 ENTRYPOINT ["spleeter"]