revert guzzle dev dep

Author: soyuka

composer.json

@@ -42,6 +42,7 @@
         "friends-of-behat/mink-browserkit-driver": "^1.3.1",
         "friends-of-behat/mink-extension": "^2.2",
         "friends-of-behat/symfony-extension": "^2.1",
+        "guzzlehttp/guzzle": "^6.0 || ^7.0",
         "jangregor/phpstan-prophecy": "^1.0",
         "justinrainbow/json-schema": "^5.2.1",
         "phpdocumentor/reflection-docblock": "^3.0 || ^4.0 || ^5.1",