chore(package): update eslint-plugin-ember to version 8.4.0

Closes #26

Author: greenkeeper[bot]

package.json

@@ -50,7 +50,7 @@
     "ember-scroll-to": "^0.6.4",
     "ember-source": "~2.18.0",
     "ember-truth-helpers": "^2.0.0",
-    "eslint-plugin-ember": "^5.0.0",
+    "eslint-plugin-ember": "^8.4.0",
     "eslint-plugin-node": "^6.0.0",
     "loader.js": "^4.2.3",
     "milligram-sass": "^1.3.0"