Install libffi in the slim images

* Seems to have gotten lost somewhere along the way

Author: JayH5

2/slim/Dockerfile

@@ -10,6 +10,7 @@ ENV LANG C.UTF-8
 RUN apt-get update && apt-get install -y --no-install-recommends \
 		ca-certificates \
 		libexpat1 \
+		libffi6 \
 		libsqlite3-0 \
 	&& rm -rf /var/lib/apt/lists/*
 

3/slim/Dockerfile

@@ -10,6 +10,7 @@ ENV LANG C.UTF-8
 RUN apt-get update && apt-get install -y --no-install-recommends \
 		ca-certificates \
 		libexpat1 \
+		libffi6 \
 		libsqlite3-0 \
 	&& rm -rf /var/lib/apt/lists/*