ran npm i @actions/core --save-dev

Author: sarahs

package.json

@@ -77,6 +77,7 @@
     "webpack-cli": "^3.3.12"
   },
   "devDependencies": {
+    "@actions/core": "^1.2.6",
     "ajv": "^6.11.0",
     "async": "^3.2.0",
     "await-sleep": "0.0.1",