Changing variables in ViewModel clones are propagated

[samuelnogueira]

By default, \Zend\View\Model\ViewModel::$variables is a \Zend\View\Variables instance.
When cloning an instance of ViewModel, if $variables property is a reference to an object instead of a native php array, calling setVariables on the clone will also change the variables in the original ViewModel instance.
This becomes a problem when using zend-view as a view renderer in Zend Expressive on a long-running process (see https://github.com/zendframework/zend-expressive-zendviewrenderer/blob/2.0.0/src/ZendViewRenderer.php#L319), and causes layout variables to be stuck in the same value between requests.

How to reproduce:

<?php
use \Zend\View\Model\ViewModel;

$viewModel1 = new ViewModel();
$viewModel1->setVariables(['a' => 'foo']);

$viewModel2 = clone $viewModel1;
$viewModel2->setVariables(['a' => 'bar']);

echo $viewModel1->a;

// outputs 'bar'
// expected output is 'foo'

[weierophinney]

Fixed with #158, to release with 2.11.0.