test against slim-http instead of slim v3

Author: danopz

composer.json

@@ -18,7 +18,7 @@
     "require-dev": {
         "zendframework/zend-diactoros": "^1.0",
         "guzzlehttp/psr7": "^1.0",
-        "slim/slim": "^3.0",
+        "slim/http": "^0.3",
         "nyholm/psr7": "dev-master"
     },
     "autoload": {