Type\Intersection does not work for > 3 types

Hi

Related to #6 

```php
$foo = Type\intersection(
    Type\instance_of(Foo::class),
    Type\instance_of(Bar::class),
    Type\instance_of(Baz::class),
    Type\instance_of(Boo::class),
)->assert($foo);
```

the type of `$foo` 
should be: `Foo&Bar&Baz&Boo`
but is: `(Foo&Bar)|(Baz&Boo)`

Thanks