🐳 Move EXTERNAL_UID closer to its use (perf)

Signed-off-by: mathieu.brunot <mathieu.brunot@monogramm.io>

docker/devenv/Dockerfile

@@ -1,7 +1,6 @@
 FROM debian:buster
 LABEL maintainer="Andrey Antukh <niwi@niwi.nz>"
 
-ARG EXTERNAL_UID=1000
 ARG DEBIAN_FRONTEND=noninteractive
 
 ENV NODE_VERSION=v12.14.1 \
@@ -53,6 +52,8 @@ RUN curl https://www.postgresql.org/media/keys/ACCC4CF8.asc | sudo apt-key add -
 COPY files/bashrc /root/.bashrc
 COPY files/vimrc /root/.vimrc
 
+ARG EXTERNAL_UID=1000
+
 RUN set -ex; \
     useradd -m -g users -s /bin/zsh -u $EXTERNAL_UID uxbox; \
     passwd uxbox -d; \