Updated phpspec


Note that this PR removes support for custom matchers which used to be implemented as following:

```php
        $initializer->initialize(new Specification('stdClass', new \ReflectionClass('stdClass')), $matchers);

        $trace = debug_backtrace();
        if (array_key_exists('class', $trace[1])) {
            $class = $trace[1]['class'];
            if (method_exists($class, 'getMatchers')) {
                $customMatchersInitializer = new CustomMatchersInitializer();
                $customMatchersInitializer->initialize(new Specification($class, new \ReflectionClass($class)), $matchers);
            }
        }
```

I'm not sure how (if possible) it should be done with the latest version of phpspec.

Working example: https://github.com/jakzal/12tdds/blob/master/spec/Day10/PhoneListSpec.php#L14