Fix interpolate bug

Testing code:

```
<html>
<head>
<script src="avalon.js"></script>
</head>
<body>
<div ms-controller="function">
<input ms-model="nick" />
<p>{%qq()%}</p>
</div>
<script>
avalon.config({
   interpolate: ["{%", "%}"]
})
	
avalon.ready(function()
{
	avalon.define("function", function(vm) {
		vm.nick = "司徒正美"
		vm.qq = function() {
			return vm.nick + "是群主";
		}
	});
	avalon.scan();
});
</script>
</body>
</html>
```