Routing/Route/Route.php should typecast extensions to an array in constructor

Currently Routing/Route/Route.php typecasts extensions to an array when setting via the extensions() method, but not when they are set in the constructor.

Example:
```js
$routes->connect('/document/:docId', [
		'controller' => 'Documents',
		'action' => 'view'
	], [
		'pass' => ['docId'],
		'_ext' => 'json'
	]);
```
Merge pull request #4627 from dakota/patch-7

Routing/Route/Route.php should typecast extensions to an array in constructor