Update to Zend Stratigility 1.3

* Fix dependency version constraint. (Reverts #1066.)
* Allow exceptions to be raised when dispatching middleware.
* Fix our error handler middleware (do not implement Stratigility's
  error handler interface, catch exceptions instead).

See https://docs.zendframework.com/zend-stratigility/migration/to-v2/.

Closes #1069.

src/Api/Middleware/HandleErrors.php

@@ -11,12 +11,12 @@
 
 namespace Flarum\Api\Middleware;
 
+use Exception;
 use Flarum\Api\ErrorHandler;
 use Psr\Http\Message\ResponseInterface as Response;
 use Psr\Http\Message\ServerRequestInterface as Request;
-use Zend\Stratigility\ErrorMiddlewareInterface;
 
-class HandleErrors implements ErrorMiddlewareInterface
+class HandleErrors
 {
     /**
      * @var ErrorHandler
@@ -32,10 +32,19 @@ class HandleErrors implements ErrorMiddlewareInterface
     }
 
     /**
-     * {@inheritdoc}
+     * Catch all errors that happen during further middleware execution.
+     *
+     * @param Request $request
+     * @param Response $response
+     * @param callable $out
+     * @return Response
      */
-    public function __invoke($e, Request $request, Response $response, callable $out = null)
+    public function __invoke(Request $request, Response $response, callable $out = null)
     {
-        return $this->errorHandler->handle($e);
+        try {
+            return $out($request, $response);
+        } catch (Exception $e) {
+            return $this->errorHandler->handle($e);
+        }
     }
 }