Add GIT_SUBMODULE_STRATEGY variable

Add GIT_SUBMODULE_STRATEGY variable to start git submodule for gitlab-ci, More detail to https://docs.gitlab.com/ee/ci/git_submodules.html#using-git-submodules-in-your-ci-jobs.
Remove git submodule script: git submodule init && git submodule update.

Author: Pengxn

.gitlab-ci.yml

@@ -6,9 +6,11 @@ stages:
   - test
   - build
 
+variables:
+  GIT_SUBMODULE_STRATEGY: recursive
+
 before_script:
-  - npm install
-  - git submodule init && git submodule update
+  - npm i
 
 test:
   stage: test