[Tests] use npx aud in posttest

Author: ljharb

package.json

@@ -16,6 +16,7 @@
     "test": "npm run tests-only",
     "pretests-only": "node test-core-js",
     "tests-only": "tape test/*.js",
+    "posttest": "npx aud --production",
     "coverage": "nyc npm run tests-only"
   },
   "testling": {