Try out Git strategy

- To avoid recloning of repo <-> changing SHA of reqirements.txt?
- See GIT_STRATEGY: fetch

.gitlab-ci.yml

 # image: docker:stable
 variables:
+  GIT_STRATEGY: fetch
   # DOCKER_TLS_CERTDIR: ""
   # DOCKER_HOST: tcp://docker:2375
   # DOCKER_DRIVER: overlay2