no pip cache in docker build, compressed docker image is 70MB smaller

Dockerfile.openpilot

@@ -52,14 +52,14 @@ ENV PATH="/root/.pyenv/bin:/root/.pyenv/shims:${PATH}"
 RUN pyenv install 3.8.2 && pyenv global 3.8.2
 RUN pyenv rehash
 
-RUN pip install pipenv==2018.11.26
+RUN pip install --no-cache-dir pipenv==2018.11.26
 
 COPY Pipfile Pipfile.lock /tmp/
 
 RUN cd /tmp && pipenv install --system --deploy
 
 # Install subset of dev dependencies needed for CI
-RUN pip install matplotlib==3.1.1 dictdiffer==0.8.0 fastcluster==1.1.25 aenum==2.2.1 lru-dict==1.1.6 scipy==1.4.1 tenacity==5.1.1 azure-common==1.1.23 azure-nspkg==3.0.2 azure-storage-blob==2.1.0 azure-storage-common==2.1.0 azure-storage-nspkg==3.1.0 pycurl==7.43.0.3 coverage==5.1
+RUN pip install --no-cache-dir matplotlib==3.1.1 dictdiffer==0.8.0 fastcluster==1.1.25 aenum==2.2.1 lru-dict==1.1.6 scipy==1.4.1 tenacity==5.1.1 azure-common==1.1.23 azure-nspkg==3.0.2 azure-storage-blob==2.1.0 azure-storage-common==2.1.0 azure-storage-nspkg==3.1.0 pycurl==7.43.0.3 coverage==5.1
 
 ENV PYTHONPATH /tmp/openpilot:${PYTHONPATH}