Allow installs of zend-diactoros 2

Author: driesvints

composer.json

@@ -29,7 +29,7 @@
         "league/oauth2-server": "^7.0",
         "phpseclib/phpseclib": "^2.0",
         "symfony/psr-http-message-bridge": "~1.0",
-        "zendframework/zend-diactoros": "~1.0"
+        "zendframework/zend-diactoros": "~1.0|~2.0"
     },
     "require-dev": {
         "mockery/mockery": "~1.0",