Add support for Symfony 5

Adds support for Symfony 5 and thus Laravel 7 as well.

Author: jkudish

composer.json

@@ -25,8 +25,8 @@
     "php": "^7.1.3",
     "ext-curl": "*",
     "jms/serializer": "^1.0|^2.0|^3.0",
-    "symfony/event-dispatcher": "^2.3|^3.0|^4.0",
-    "symfony/yaml": "^2.3|^3.0|^4.0",
+    "symfony/event-dispatcher": "^2.3|^3.0|^4.0|^5.0",
+    "symfony/yaml": "^2.3|^3.0|^4.0|^5.0",
     "guzzlehttp/guzzle": "^6.0",
     "doctrine/collections": "^1.2"
   },