update gitlab tests to run on newer node versions

.gitlab-ci.yml

@@ -22,8 +22,12 @@ cache:
   paths:
   - node_modules/
 
-test:6:
-  image: node:6-alpine
+test:8:
+  image: node:8-alpine
+  script: yarn run test
+
+test:9:
+  image: node:9-alpine
   script: yarn run test
 
 test:latest: