Merge branch 'patch-1' into 'master'

Update .gitlab-ci.yml for submodule management

See merge request pages/hugo!52

.gitlab-ci.yml

 # All available Hugo versions are listed here: https://gitlab.com/pages/hugo/container_registry
 image: registry.gitlab.com/pages/hugo:latest
 
+variables:
+  GIT_SUBMODULE_STRATEGY: recursive
+
 test:
   script:
   - hugo