chore(package): update ember-ajax to version 4.0.2

Closes #20

Author: greenkeeper[bot]

package.json

@@ -25,7 +25,7 @@
   },
   "devDependencies": {
     "broccoli-asset-rev": "^2.4.5",
-    "ember-ajax": "^3.0.0",
+    "ember-ajax": "^4.0.2",
     "ember-cli": "~2.18.0",
     "ember-cli-code-coverage": "^1.0.0-beta.1",
     "ember-cli-dependency-checker": "^2.0.0",