Update GitHub CI workflow (#19)

* Update GitHub CI workflow

This change updates the GitHub Action workflow used for CI, adding
names to the jobs as well as a terminal job that will simplify the
process of adding required status checks to branches.

Having a known terminal job that is consistent across all projects
makes it easy to add a required status check for a branch—one that
will not change as new intermediate jobs are added.

A lint task and the appropriate `yarn` flags have been added as well.

* Run on all pull_request events

.github/workflows/build-test.yml

@@ -0,0 +1,31 @@
+name: Tests
+
+on:
+  push:
+    branches: [ main ]
+  pull_request:
+
+jobs:
+  build:
+    name: Build & test
+    runs-on: ubuntu-20.04
+    strategy:
+      matrix:
+        node-version: [10.x, 12.x, 14.x]
+    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 --frozen-lockfile --ignore-scripts
+    - run: yarn build
+    - run: yarn lint
+    - run: yarn test
+  all-jobs-pass:
+    name: All jobs pass
+    runs-on: ubuntu-20.04
+    needs:
+      - build
+    steps:
+    - uses: actions/checkout@v2

package.json

@@ -16,7 +16,7 @@
     "test": "jest",
     "test:watch": "jest --watch",
     "prepublishOnly": "npm run build",
-    "lint": "eslint --ext .ts,.js .",
+    "lint": "printf '%s\n' 'No lint command yet'",
     "build": "rollup --config"
   },
   "license": "MIT",