[Mobilizon] Fix cross-compilation of deps

May come back to alpine in the future

pica-mobilizon/app/Dockerfile

@@ -35,14 +35,17 @@ RUN rm -rf ./.dockerignore ./.gitignore ./.gitlab-ci.yml ./CHANGELOG.md ./CONTRI
         && mv GeoLite2-City.mmdb /home/mobilizon/build/priv/data/GeoLite2-City.mmdb
 
 # Final docker image
-FROM elixir:1.10.4-alpine
+FROM elixir:1.10.4-slim
 ENV INIT=FALSE \
 	ADMIN_EMAIL=test@test.com \
 	ADMIN_PASSWORD=passwd \
 	MIX_ENV=prod \
 	INSTANCE_CONFIG=prod
-RUN addgroup -S mobilizongr && adduser -s /bin/bash -S mobilizon -G mobilizongr
-RUN apk update && apk add --update git && rm -rf /tmp/* /var/tmp/*
+RUN useradd -ms /bin/bash -p ! mobilizon  \
+        && apt-get update \
+ 	&& apt-get install -y git \
+        && apt-get clean \
+        && rm -rf /var/lib/apt/lists/* /tmp/* /var/tmp/*
 COPY --from=builder /home/mobilizon/build/ /home/mobilizon/live/
 COPY --from=builder /home/mobilizon/.mix/ /home/mobilizon/.mix/
 COPY ./entrypoint.sh /home/mobilizon/entrypoint.sh