Update to use RouteResultObserverInterface from zend-expressive

Following on zendframework/zend-expressive#206, this patch updates the
`UrlHelper` to implement `Zend\Expressive\RouteResultObserverInterface` instead
of `Zend\Expressive\Router\RouteResultObserverInterface`, which is now
deprecated.

Author: weierophinney

src/UrlHelper.php

@@ -10,7 +10,7 @@
 use Zend\Expressive\Router\Exception\RuntimeException;
 use Zend\Expressive\Router\RouterInterface;
 use Zend\Expressive\Router\RouteResult;
-use Zend\Expressive\Router\RouteResultObserverInterface;
+use Zend\Expressive\RouteResultObserverInterface;
 use Zend\Expressive\Template\Exception\RenderingException;
 use Zend\View\Helper\AbstractHelper;
 

test/UrlHelperTest.php

@@ -14,7 +14,7 @@
 use Zend\Expressive\Router\Exception\RuntimeException;
 use Zend\Expressive\Router\RouterInterface;
 use Zend\Expressive\Router\RouteResult;
-use Zend\Expressive\Router\RouteResultObserverInterface;
+use Zend\Expressive\RouteResultObserverInterface;
 use Zend\Expressive\Template\Exception;
 use Zend\Expressive\ZendView\UrlHelper;