add ember-on-modifier polyfill

Author: mansona

package-lock.json

@@ -64,6 +64,7 @@
     "ember-load-initializers": "^2.1.1",
     "ember-maybe-import-regenerator": "^0.1.6",
     "ember-native-dom-helpers": "^0.6.2",
+    "ember-on-modifier": "^1.0.1",
     "ember-percy": "^1.6.0",
     "ember-qunit": "^4.6.0",
     "ember-resolver": "^7.0.0",