fix(CSSClass): change selector to ng-class

BREAKING CHANGE:

The selector for the CSSClass directive was changed
from [class] to [ng-class]. The directive itself was
renamed from CSSClass to NgClass

Closes #3498

modules/angular2/docs/core/01_templates.md

@@ -94,7 +94,7 @@ Example:
 
 <pre>
 ```
-<div [class]="stringify(selected)">
+<div [title]="stringify(selected)">
 ```
 </pre>
       </td>