set default rstudio password

Dockerfile

@@ -3,6 +3,8 @@ FROM rocker/tidyverse
 LABEL version="0.01" 
 LABEL maintainer="Théophile Sanchez <theophile.sanchez@wsl.ch>"
 
+ENV USER="rstudio" PASSWORD="rstudio" ROOT="TRUE"
+
 RUN sudo apt-get update
 
 # dependencies required by dada2