add prepublish build step

Author: keithamus

package.json

@@ -27,6 +27,7 @@
     "lint": "eslint . --ignore-path .gitignore",
     "pretest": "npm run build",
     "test": "npm run lint && karma start test/karma.config.cjs",
+    "prepublish": "npm run build",
     "postpublish": "npm publish --ignore-scripts --@github:registry='https://npm.pkg.github.com'"
   },
   "prettier": "@github/prettier-config",