fix: typo in CI script

.gitlab-ci.yml

 services:
-  - docker:19.03.1-dind
+  - name: docker:19.03.0-dind
     command: ["--mtu=1458"]
+    
+variables:
+    DOCKER_DRIVER: overlay2
+    DOCKER_TLS_CERTDIR: ""
 
 stages:
   - build-image
@@ -9,9 +13,6 @@ stages:
 build-testing-image:
   stage: build-image
   image: docker:19.03.1
-  variables:
-    DOCKER_DRIVER: overlay2
-    DOCKER_TLS_CERTDIR: ""
   tags: 
     - privileged
   before_script:
@@ -47,4 +48,3 @@ run-drake:
     - ./make.R
     - zip -r artifacts/drake_cache.zip .drake
   when: always
-