Update code to comply with Ember 2.8.0.

Check discussion in emberjs/ember.js#14266

addon/components/md-card-content.js

@@ -1,6 +1,5 @@
 import Component from '@ember/component';
 import { computed } from '@ember/object';
-import { alias } from '@ember/object/computed';
 import layout from '../templates/components/md-card-content';
 
 export default Component.extend({
@@ -9,9 +8,18 @@ export default Component.extend({
   classNames: ['card-content'],
 
   classNameBindings: ['class'],
-  title: alias('parentView.title'),
-  titleClass: alias('parentView.titleClass'),
-  activator: alias('parentView.activator'),
+
+  title: computed(function() {
+    return this.get('parentView.title');
+  }).volatile(),
+
+  titleClass: computed(function() {
+    return this.get('parentView.titleClass');
+  }).volatile(),
+
+  activator: computed(function() {
+    return this.get('parentView.activator');
+  }),
 
   cardTitleClass: computed('titleClass', function() {
     return this.get('titleClass') || 'black-text';