Prevent modified twice in single render in Ember 2.9

Fixes

```
Error: Assertion Failed: You modified activeStates.disabled twice in a single render. This was unreliable and slow in Ember 1.x and is no longer supported. See emberjs/ember.js#13948 for more details.
```

in Ember 2.9

addon/templates/components/demo--ui-checkbox.hbs

@@ -1,5 +1,5 @@
 {{!- BEGIN-SNIPPET demo--ui-checkbox -}}
-{{#ui-checkbox _activeStates=activeStates kind=kind size=size disabled=activeStates.disabled error=activeStates.error}}
+{{#ui-checkbox _activeStates=activeStates kind=kind size=size}}
   {{size}}
 {{/ui-checkbox}}
 {{!- END-SNIPPET -}}