iOS Center Button for tabGroup

index.js

var btnAction = Ti.UI.createButton({
	title:"I'm a button",
	backgroundColor:"#e7e7e8",
	width:85, height:55, bottom:0, borderColor:"#999"
});

$.tbgroup.add(btnAction);
$.tbgroup.open();

index.xml

<Alloy>
	<TabGroup id="tbgroup">
		<Tab icon="KS_nav_views.png">
			<Window title="Tab 1">
				<Label>I am Window 1</Label>
			</Window>
		</Tab>
		<Tab icon="KS_nav_views.png">
			<Window title="Tab 2">
				<Label>I am Window 2</Label>
			</Window>
		</Tab>
		<Tab icon="KS_nav_views.png">
			<Window title="Tab 3">
				<Label>I am Window 3</Label>
			</Window>
		</Tab>		
		<Tab icon="KS_nav_views.png">
			<Window title="Tab 4">
				<Label>I am Window 4</Label>
			</Window>
		</Tab>	
		<Tab icon="KS_nav_views.png">
			<Window title="Tab 5">
				<Label>I am Window 5</Label>
			</Window>
		</Tab>			
	</TabGroup>
</Alloy>