chore(package): update ember-ajax to version 4.0.1

Closes #1739

Author: greenkeeper[bot]

package.json

@@ -18,7 +18,7 @@
   "devDependencies": {
     "broccoli-asset-rev": "^2.4.5",
     "coveralls": "^3.0.0",
-    "ember-ajax": "^3.0.0",
+    "ember-ajax": "^4.0.1",
     "ember-auto-focus": "^2.0.1",
     "ember-autoresize": "1.0.0",
     "ember-can": "^0.8.4",