make docker build 2 stage

Dockerfile

@@ -4,10 +4,13 @@ RUN apt-get update && \
     apt-get install -y python3-pip gpgv1 gnupg1 gpg sudo wget git && \
     useradd artifact
 
+ADD requirements.txt /tmp/requirements.txt
+
+RUN pip3 install -r /tmp/requirements.txt
+
 ADD . /tmp/code
 
 RUN cd /tmp/code && \
-    pip3 install -r requirements.txt && \
     python3 setup.py install
 
 USER artifact