ci: Use all cores for R package installation

Change-Id: I42b6020133312bfc4ded9c5831bd3b88c37e3957
diff --git a/.gitlab-ci.yml b/.gitlab-ci.yml
index 8e41ab7..1ba74f3 100644
--- a/.gitlab-ci.yml
+++ b/.gitlab-ci.yml
@@ -47,6 +47,7 @@
     - R -e "install.packages(c('devtools', 'scales', 'sp', 'raster', 'kableExtra', 'DT', 'svglite', 'qrcode'))"
     - R -e 'devtools::install_git("https://korap.ids-mannheim.de/gerrit/IDS-Mannheim/idsThemeR")'
     - R -e 'devtools::install_git("https://korap.ids-mannheim.de/gerrit/IDS-Mannheim/posterdown")'
+    - echo "options(Ncpus=$(nproc))" > ~/.Rprofile
     - end_section install_r_packages
 
   script: