Add coveralls

.coveralls.yml

@@ -0,0 +1 @@
+repo_token: ghY6fJL969V76s6h7V40zsF2UUAagYacP

.github/workflows/coveralls.yml

@@ -0,0 +1,27 @@
+on: ["push", "pull_request"]
+
+name: Coveralls
+
+jobs:
+
+  build:
+    name: Build
+    runs-on: ubuntu-latest
+    steps:
+
+    - uses: actions/checkout@v1
+
+    - name: Use Node.js 12.x
+      uses: actions/setup-node@v1
+      with:
+        node-version: 12.x
+
+    - name: npm install, npm run coveralls
+      run: |
+        npm install
+        npm run coveralls
+
+    - name: Coveralls
+      uses: coverallsapp/github-action@master
+      with:
+        github-token: ${{ secrets.GITHUB_TOKEN }}

package.json

@@ -8,7 +8,8 @@
   "main": "index.js",
   "scripts": {
     "test": "jest --coverage",
-    "lint": "standard --fix"
+    "lint": "standard --fix",
+    "coveralls": "jest --coverage --coverageReporters=lcov --coverageDirectory=./coverage"
   },
   "engines": {
     "node": "8.10.0"