fix(ci): make sure to clone tinymce submodule

.gitlab-ci.yml

@@ -3,6 +3,9 @@ stages:
   - build
   - deploy
 
+variables:
+  GIT_SUBMODULE_STRATEGY: recursive
+
 # define the build stage
 build_stage:
   stage: build
@@ -60,3 +63,4 @@ deploy_production:
   only:
     - tags
   # restrict to specific branch
+