Update minimum version of guzzlehttp/guzzle to 5.3.3 as it supports PHP 7.3

Author: michalbundyra

composer.json

@@ -22,7 +22,7 @@
     },
     "require-dev": {
         "doctrine/migrations": "^1.0",
-        "guzzlehttp/guzzle": "^5.3.2 || ^6.3.3",
+        "guzzlehttp/guzzle": "^5.3.3 || ^6.3.3",
         "mikey179/vfsStream": "^1.6",
         "php-amqplib/php-amqplib": "^2.0",
         "phpunit/phpunit": "^5.7.27 || 6.5.8 || ^7.1.2",