Less Docker layers

Dockerfile

@@ -1,27 +1,20 @@
 FROM ubuntu:16.04
 MAINTAINER Stéphane Brunner <stephane.brunner@camptocamp.com>
 
+COPY . /src/
 RUN \
   apt-get update && \
-  apt-get install --assume-yes --no-install-recommends wget ca-certificates python python-mapnik mapnik-utils gdal-bin libpq5 libgeos-c1v5 fonts-dejavu node-carto osm2pgsql curl unzip && \
+  apt-get install --assume-yes --no-install-recommends wget ca-certificates python python-mapnik mapnik-utils gdal-bin libpq5 libgeos-c1v5 fonts-dejavu node-carto osm2pgsql curl unzip gcc python-dev libpq-dev libgeos-dev libmapnik-dev && \
   cd /tmp && \
   wget https://bootstrap.pypa.io/get-pip.py && \
   python get-pip.py && \
   mkdir /fonts && \
   mkdir /project && \
-  apt-get remove --assume-yes --purge wget ca-certificates && \
-  apt-get clean && \
-  rm -rf /var/lib/apt/lists/* /tmp/* /var/tmp/* /root/.cache/*
-
-COPY . /src/
-RUN \
-  apt-get update && \
-  apt-get install --assume-yes --no-install-recommends gcc python-dev libpq-dev libgeos-dev libmapnik-dev && \
   cd /src && \
   mv docker/run /usr/bin/ && \
   pip install -r requirements.txt && \
   pip install . && \
-  apt-get remove --assume-yes --purge gcc python-dev libpq-dev libgeos-dev libmapnik-dev && \
+  apt-get remove --assume-yes --purge gcc python-dev libpq-dev libgeos-dev libmapnik-dev wget && \
   apt-get autoremove --assume-yes && \
   apt-get clean && \
   rm -rf /src /var/lib/apt/lists/* /tmp/* /var/tmp/* /root/.cache/*