3.8: Install gcc and libffi-dev otherwise Poetry does not get installed

- as cffi dependency needs to be compiled
- Could be removed later when fixed upstream (cffi, poetry)
- In order to lighten the image and to speed-up the job

3.8/Dockerfile

@@ -2,7 +2,7 @@ FROM python:3.8-rc-slim-buster
 
 # Install libsodium
 RUN apt update
-RUN apt install --yes libsodium23 black
+RUN apt install --yes libsodium23 libffi-dev gcc black
 
 # Install Poetry
 RUN pip3 install poetry --pre