ESLint: Be explicit with Ember Data attribute types

no issue
- https://github.com/ember-cli/eslint-plugin-ember/blob/master/docs/rules/no-empty-attrs.md

ghost/admin/app/models/post.js

@@ -101,7 +101,7 @@ export default Model.extend(Comparable, ValidationEngine, {
     status: attr('string', {defaultValue: 'draft'}),
     title: attr('string', {defaultValue: ''}),
     updatedAtUTC: attr('moment-utc'),
-    updatedBy: attr(),
+    updatedBy: attr('number'),
     url: attr('string'),
     uuid: attr('string'),
 

ghost/admin/app/models/role.js

@@ -8,8 +8,8 @@ export default Model.extend({
     description: attr('string'),
     createdAtUTC: attr('moment-utc'),
     updatedAtUTC: attr('moment-utc'),
-    createdBy: attr(),
-    updatedBy: attr(),
+    createdBy: attr('number'),
+    updatedBy: attr('number'),
 
     lowerCaseName: computed('name', function () {
         return this.get('name').toLocaleLowerCase();

ghost/admin/app/models/tag.js

@@ -11,15 +11,15 @@ export default Model.extend(ValidationEngine, {
     name: attr('string'),
     slug: attr('string'),
     description: attr('string'),
-    parent: attr(),
+    parent: attr('string'), // unused
     metaTitle: attr('string'),
     metaDescription: attr('string'),
     featureImage: attr('string'),
     visibility: attr('string', {defaultValue: 'public'}),
     createdAtUTC: attr('moment-utc'),
     updatedAtUTC: attr('moment-utc'),
-    createdBy: attr(),
-    updatedBy: attr(),
+    createdBy: attr('number'),
+    updatedBy: attr('number'),
     count: attr('raw'),
 
     isInternal: equal('visibility', 'internal'),

ghost/admin/mirage/factories/user.js

@@ -17,7 +17,7 @@ export default Factory.extend({
     status: 'active',
     tour: null,
     updatedAt: '2015-11-02T16:12:05.000Z',
-    updatedBy: '2015-09-02T13:41:50.000Z',
+    updatedBy: '1',
     website: 'http://example.com',
     roles() { return []; }
 });