ci(CircleCI): run tests on both node 8 and 9

.circleci/config.yml

@@ -1,7 +1,7 @@
 # https://circleci.com/docs/2.0/language-javascript/
 version: 2
 jobs:
-  build:
+  "node-8":
     docker:
       - image: circleci/node:8
     working_directory: ~/typescript-starter
@@ -20,4 +20,29 @@ jobs:
           key: v1-dependencies-{{ checksum "package.json" }}
       - run: npm test
       - run: npx nyc report --reporter=lcov | npx codecov
-      - run: npm run cov:check
+      - run: npm run cov:check
+  "node-latest":
+    docker:
+      - image: circleci/node:latest
+    working_directory: ~/typescript-starter
+    steps:
+      - checkout
+      - restore_cache:
+          keys:
+          - v1-dependencies-{{ checksum "package.json" }}
+          - v1-dependencies-
+      - run: npm install
+      - save_cache:
+          paths:
+            - node_modules
+          key: v1-dependencies-{{ checksum "package.json" }}
+      - run: npm test
+      - run: npx nyc report --reporter=lcov | npx codecov
+      - run: npm run cov:check
+
+workflows:
+  version: 2
+  build:
+    jobs:
+      - "node-8"
+      - "node-latest"