Route matching must be anchored to the start of the string

I think the reason for using a regex in rules maching is to match child routes.
So we must anchor the regex to the start of the string.

Example : I want to deny access for this parent route ```webFoo``` :
```php
'firewalls' => array(
    'ZfcRbac\Firewall\Route' => array(
        array('route' => 'webFoo', 'permissions' => 'myperms'),
    ),
);
```

 It will also match ```webFoo/bar``` and ```webFoo/baz```.
But infortunately, if i don't anchor the regex, it will also match ```otherRouter/mywebFoo```.