[update] Officially drop Node v4

Author: pzuraq

package.json

@@ -109,7 +109,7 @@
     "qunit-dom": "^0.5.0"
   },
   "engines": {
-    "node": "^4.5 || 6.* || >= 7.*"
+    "node": "6.* || >= 7.*"
   },
   "ember-addon": {
     "configPath": "tests/dummy/config",