ci: run tests on node 8 and node 10

Author: evanlucas

.gitlab-ci.yml

@@ -7,8 +7,8 @@ before_script:
   - echo "//registry.npmjs.org/:_authToken=${NPM_TOKEN}" > .npmrc
   - npm install
 
-test:node6:
-  image: gcr.io/help-1272/node:6
+test:node10:
+  image: gcr.io/help-1272/node:10
   stage: test
   script:
     - npm test -- --coverage-report=text-summary