publish to GPR as a postpublish step

package.json

@@ -13,7 +13,8 @@
     "build": "rollup -c && cp src/task-lists-element.js.flow dist/index.esm.js.flow && cp src/task-lists-element.js.flow dist/index.umd.js.flow",
     "pretest": "npm run build",
     "test": "karma start test/karma.config.js",
-    "prepublishOnly": "npm run build"
+    "prepublishOnly": "npm run build",
+    "postpublish": "npm publish --ignore-scripts --@github:registry='https://npm.pkg.github.com'"
   },
   "keywords": [
     "task",