Add Github CI for linting and tests

.github/workflows/tests.yml

+name: CI
+
+on: [push, pull_request]
+
+jobs:
+  lint:
+   runs-on: ubuntu-latest
+   steps:
+    - uses: actions/checkout@v2
+    - name: Use Node.js
+      uses: actions/setup-node@v1
+      with:
+        node-version: 14
+    - run: yarn
+    - run: yarn lint
+  test:
+    runs-on: ubuntu-latest
+    strategy:
+      matrix:
+        node_version: [12, 14, 16]
+    steps:
+      - uses: actions/checkout@v2
+      - name: Use Node.js ${{ matrix.node_version }}
+        uses: actions/setup-node@v1
+        with:
+          node-version: ${{ matrix.node_version }}
+      - run: yarn
+      - run: yarn test