[Mobilizon] Fix image upload

pica-mobilizon/app/Dockerfile

@@ -43,7 +43,7 @@ ENV INIT=FALSE \
 	INSTANCE_CONFIG=prod
 RUN useradd -ms /bin/bash -p ! mobilizon  \
         && apt-get update \
- 	&& apt-get install -y git \
+ 	&& apt-get install -y git file\
         && apt-get clean \
         && rm -rf /var/lib/apt/lists/* /tmp/* /var/tmp/*
 COPY --from=builder /home/mobilizon/build/ /home/mobilizon/live/