Update integration tests

Author: Nyholm

composer.json

@@ -18,7 +18,7 @@
     "require-dev": {
         "phpunit/phpunit": "^4.8",
         "guzzlehttp/psr7": "^1.2",
-        "php-http/adapter-integration-tests": "~0.3.1",
+        "php-http/adapter-integration-tests": "^0.4",
         "php-http/message": "^1.0",
         "php-http/client-common": "^1.0"
     },