ci: use rocker/geospatial and reorganise package installation

.gitlab-ci.yml

 stages:
-    - checks
-    - website
+  - install
+  - checks
+  - website
 
 default:
   tags: [docker]
 
-image: rocker/verse:latest
-
-cache:
-  paths:
-    - "$CI_PROJECT_DIR/ci/lib/"
+image: rocker/geospatial:latest
 
 variables:
   R_LIBS_USER: "$CI_PROJECT_DIR/ci/lib"
@@ -23,8 +20,12 @@ cache:
 before_script:
   - mkdir -p $R_LIBS_USER $BUILD_LOGS_DIR
   - echo "R_LIBS='$R_LIBS_USER'" > .Renviron
-  - sudo apt-get update && sudo apt-get install -y libudunits2-dev
-  - R -q -e 'devtools::install_deps(dep = T)'
+
+install:
+  stage: install
+  script:
+    - R -q -e 'devtools::install_deps(dependencies = TRUE, repos = "http://cran.r-project.org", build = TRUE)'
+    - R -q -e 'devtools::install(quick = TRUE)'
 
 .check:
   stage: checks
@@ -60,9 +61,6 @@ bookdown:
       - dev
       - tags
   script:
-    - sudo apt-get update && sudo apt-get install -y proj-bin libgdal-dev libgeos-dev
-    - R -q -e 'devtools::install_deps(dependencies = TRUE, repos = "http://cran.r-project.org", build = TRUE)'
-    - R -q -e 'devtools::install(quick = TRUE)'
     - cd bookdown
     - R -q -e 'bookdown::render_book()'
     - sudo apt-get update && sudo apt-get install -y sshpass rsync