add ember-decorators polyfill

Author: mansona

package-lock.json

@@ -57,6 +57,7 @@
     "ember-cli-sri": "^2.1.1",
     "ember-cli-stylelint": "^4.0.0",
     "ember-cli-uglify": "^3.0.0",
+    "ember-decorators-polyfill": "^1.1.5",
     "ember-disable-prototype-extensions": "^1.1.3",
     "ember-export-application-global": "^2.0.1",
     "ember-fetch": "^8.0.1",