Require http-interop/http-middleware 0.4.1

Since the newest versions of zend-stratigility and
zend-expressive-router each now depend on
webimpress/http-middleware-compatibility, http-interop/http-middleware
is no longer a required package. As such, new installations fail, as
this package is necessary in order to run Expressive.

This patch adds the package with a constraint of ^0.4.1 in order to fix
issues on the existing 2.0.X branch.

composer.json

@@ -27,6 +27,7 @@
     "require": {
         "php": "^5.6 || ^7.0",
         "fig/http-message-util": "^1.1.2",
+        "http-interop/http-middleware": "^0.4.1",
         "psr/container": "^1.0",
         "psr/http-message": "^1.0.1",
         "zendframework/zend-diactoros": "^1.3.10",