Collect coverage

- Add Coverage step to workflow
- Generate JSON coverage report
- Ignore coverage folder

.github/workflows/main.yml

@@ -21,4 +21,7 @@ jobs:
         run: npm run lint
 
       - name: Test
-        run: npm test
+        run: npm test -- --coverage-report=json
+
+      - name: Coverage
+        uses: codecov/codecov-action@v1

.gitignore

@@ -1,3 +1,4 @@
 .nyc_output
+coverage
 node_modules
 npm-debug.log

.prettierignore

@@ -1 +1,3 @@
+.nyc_output
+coverage
 tap-snapshots