Switch merge order in View\Environment::make()

As mentioned in my last comment on #1095, the recent change to accept a third parameter is merged in the wrong order - variables defined in the parent view override those passed as a parameter. This ensures variables passed to `@include()` override the variables from the calling view.

I couldn't work out how to write a unit test for this, but here is a simple example:

```html+php
<?php $page = 1 ?>
@include('test', ['page' => 2])
```

Previously this would have `$page = 1` in the `test` view, now it has `$page = 2`.