Install libffi-dev, required for cffi

infra/dockerfile.base

@@ -3,9 +3,9 @@ FROM python:3.7.4-slim
 # Setup dependencies in a cacheable step
 COPY requirements.txt /requirements.txt
 RUN apt-get update && \
-		apt-get install -y --no-install-recommends gcc g++ libgomp1 && \
+		apt-get install -y --no-install-recommends gcc g++ libgomp1 libffi-dev && \
 		pip install --disable-pip-version-check --no-cache-dir -r /requirements.txt && \
-		apt-get remove -y gcc g++ && \
+		apt-get remove -y gcc g++ libffi-dev && \
 		apt-get autoremove -y && \
 		rm -rf /var/lib/apt/lists/*