fix ci. change node8 to node12

Author: nitaking

.circleci/config.yml

@@ -19,10 +19,10 @@ jobs:
       - run:
           name: Testing
           command: yarn test
-  node-8:
+  node-12:
     <<: *test
     docker:
-      - image: node:8
+      - image: node:12
   node-10:
     <<: *test
     docker:
@@ -56,8 +56,8 @@ workflows:
   "sequelize-tinker":
     jobs:
       - node-latest
-      - node-8
       - node-10
+      - node-12
       - cache:
           filters:
             tags: