Update CI config

.gitlab-ci.yml

 image: node:10
 
 before_script:
-  - apt --yes update
-  - apt --yes install --no-install-recommends openssh-client
-
   - npm install gitbook-cli -g
 
+  # image node:10 already provides openssh-client
+
   # Run ssh-agent (inside the build environment).
   - eval $(ssh-agent -s)
 
@@ -20,4 +19,4 @@ job:
   stage: build
   script:
     - gitbook build
-    - scp -r _book validata@dev.validata.fr:validata-doc-html
\ No newline at end of file
+    - rsync -avz --delete _book/ validata@dev.validata.fr:validata-doc-html/
\ No newline at end of file