chore(package): update ember-cli to version 3.18.0

Closes #29

Author: greenkeeper[bot]

package.json

@@ -23,7 +23,7 @@
   "devDependencies": {
     "@ember/optional-features": "^0.6.3",
     "broccoli-asset-rev": "^2.7.0",
-    "ember-cli": "~3.6.0",
+    "ember-cli": "~3.18.0",
     "ember-cli-babel": "^7.1.2",
     "ember-cli-dependency-checker": "^3.0.0",
     "ember-cli-eslint": "^4.2.3",