ci: add config

.circleci/config.yml

+version: 2
+jobs:
+  build:
+    docker:
+      # specify the version you desire here
+      - image: vuejs/ci
+
+    working_directory: ~/repo
+
+    steps:
+      - checkout
+
+      # Download and cache dependencies
+      - restore_cache:
+          keys:
+          - v1-dependencies-{{ checksum "yarn.lock" }}
+          # fallback to using the latest cache if no exact match is found
+          - v1-dependencies-
+
+      - run: yarn install
+
+      - save_cache:
+          paths:
+            - node_modules
+            - ~/.cache/yarn
+          key: v1-dependencies-{{ checksum "yarn.lock" }}
+
+      # run tests!
+      - run: yarn test