Build's context set in the app directory

Dockerfile.sample

@@ -2,14 +2,14 @@
 # with R module (install.R) and their system dependencies (apt.txt)
 FROM rocker/shiny-verse
 
-ARG SHINY_REPODIR='.'
 ARG SHINY_SERVERDIR=/srv/shiny-server
 
 USER root
 
 WORKDIR ${SHINY_SERVERDIR}
 RUN rm -r *
-COPY ${SHINY_REPODIR}/ ./
+# Build's context should be set in the App directory
+COPY ./ ./
 
 # Install packages with apt-get
 RUN if [ -f "apt.txt" ]; then \