update to newer R release; add German locale

Dockerfile

@@ -1,4 +1,4 @@
-FROM rocker/rstudio:3.5.0
+FROM rocker/rstudio:3.5.3
 
 # load shiny into rstudio image (see https://github.com/rocker-org/shiny/pull/31/)
 EXPOSE 3838
@@ -9,7 +9,11 @@ RUN export ADD="shiny" && \
 COPY ./src /srv/shiny-server/src
 
 # install system package needed for some R packages
-RUN apt-get update && apt-get install -y --no-install-recommends libssl-dev apt-utils
+RUN apt-get update && apt-get install -y --no-install-recommends libssl-dev apt-utils locales-all
+
+# use German locale (for plots and strings)
+RUN locale-gen de_DE.UTF-8
+ENV LANG='de_DE.UTF-8' LANGUAGE='de_DE:de' LC_ALL='de_DE.UTF-8'
 
 # install R packages so that they are cached (in opposite to installing them via R)
 RUN install2.r --error envDocument dplyr assertthat lubridate tidyr DBI plotly RSQLite ggplot2 chron darksky RCurl shinycssloaders brms