Updated core files to match ember-cli new output

ghost/admin/app/app.js

@@ -2,7 +2,7 @@ import 'ghost-admin/utils/link-component';
 import 'ghost-admin/utils/route';
 import Application from '@ember/application';
 import Resolver from 'ember-resolver';
-import config from './config/environment';
+import config from 'ghost-admin/config/environment';
 import loadInitializers from 'ember-load-initializers';
 import {registerWarnHandler} from '@ember/debug';
 

ghost/admin/app/router.js

@@ -1,5 +1,5 @@
 import EmberRouter from '@ember/routing/router';
-import config from './config/environment';
+import config from 'ghost-admin/config/environment';
 import ghostPaths from 'ghost-admin/utils/ghost-paths';
 
 const Router = EmberRouter.extend({

ghost/admin/ember-cli-update.json

@@ -0,0 +1,18 @@
+{
+    "schemaVersion": "1.0.0",
+    "packages": [
+        {
+            "name": "ember-cli",
+            "version": "3.20.0",
+            "blueprints": [
+                {
+                    "name": "app",
+                    "outputRepo": "https://github.com/ember-cli/ember-new-output",
+                    "codemodsSource": "ember-app-codemods-manifest@1",
+                    "isBaseBlueprint": true,
+                    "options": []
+                }
+            ]
+        }
+    ]
+}

ghost/admin/tests/helpers/resolver.js

@@ -1,5 +1,5 @@
 import Resolver from '../../resolver';
-import config from '../../config/environment';
+import config from 'ghost-admin/config/environment';
 
 const resolver = Resolver.create();
 

ghost/admin/tests/test-helper.js

@@ -1,5 +1,5 @@
-import Application from '../app';
-import config from '../config/environment';
+import Application from 'ghost-admin/app';
+import config from 'ghost-admin/config/environment';
 import registerWaiter from 'ember-raf-scheduler/test-support/register-waiter';
 import start from 'ember-exam/test-support/start';
 import {setApplication} from '@ember/test-helpers';