re-organise ARG

Dockerfile

@@ -3,8 +3,6 @@ FROM ubuntu:focal
 # define geographic location during R installation
 ENV TZ=Etc/UTC
 ENV DEBIAN_FRONTEND noninteractive
-ARG SHINY_SERVER_VERSION=latest
-ARG R_VERSION=latest
 
 EXPOSE 3838
 CMD ["shiny-server"]
@@ -34,13 +32,17 @@ RUN apt-get update \
 
 COPY ./scripts /opt/scripts
 
+ARG R_VERSION=latest
 #install R, along with its dependencies
 RUN /opt/scripts/install_r_cran.sh
 # test R in another layer
 RUN R -q -e "sessionInfo()"
 
-# Install R packages included Shiny, then install shiny server
+# Install R packages including Shiny
 RUN Rscript /opt/scripts/install_r_packages.R
+
+# Install shiny server
+ARG SHINY_SERVER_VERSION=latest
 RUN /opt/scripts/install_shiny_server.sh
  
 # allows trafic from all ips