add coveralls

Author: horike37

package-lock.json

@@ -25,6 +25,7 @@
     "aws-sdk": "^2.496.0",
     "chai": "^4.2.0",
     "chai-as-promised": "^7.1.1",
+    "coveralls": "^3.0.5",
     "eslint": "^6.0.1",
     "eslint-config-prettier": "^6.0.0",
     "eslint-plugin-import": "^2.18.2",