Update composer.json (#25)

Author: snapshotpl

composer.json

@@ -18,7 +18,7 @@
         "psr/http-server-middleware": "^1.0",
         "psr/container": "^1.0",
         "psr/http-message": "^1.0.1",
-        "zendframework/zend-diactoros": "^1.1.3"
+        "zendframework/zend-diactoros": "^1.1.3 || ^2.0"
     },
     "require-dev": {
         "phpunit/phpunit": "^7.1.2",