drop support for Symfony < 4.3

Author: Mathieu Lemoine

composer.json

@@ -9,16 +9,16 @@
         "php": ">=7.1",
         "enqueue/enqueue": "^0.9",
         "queue-interop/queue-interop": "^0.7|^0.8",
-        "symfony/console": "^3.4|^4|^5",
-        "symfony/process": "^3.4|^4|^5"
+        "symfony/console": "^4.3|^5",
+        "symfony/process": "^4.3|^5"
     },
     "require-dev": {
         "phpunit/phpunit": "~7.5",
-        "symfony/dependency-injection": "^3.4|^4|^5",
-        "symfony/config": "^3.4|^4|^5",
-        "symfony/http-kernel": "^3.4|^4|^5",
-        "symfony/filesystem": "^3.4|^4|^5",
-        "symfony/yaml": "^3.4|^4|^5",
+        "symfony/dependency-injection": "^4.3|^5",
+        "symfony/config": "^4.3|^5",
+        "symfony/http-kernel": "^4.3|^5",
+        "symfony/filesystem": "^4.3|^5",
+        "symfony/yaml": "^4.3|^5",
         "enqueue/null": "0.9.x-dev",
         "enqueue/fs": "0.9.x-dev",
         "enqueue/test": "0.9.x-dev"
@@ -31,7 +31,7 @@
         "docs": "https://github.com/php-enqueue/enqueue-dev/blob/master/docs/index.md"
     },
     "suggest": {
-        "symfony/dependency-injection": "^3.4|^4|^5 If you'd like to use async event dispatcher container extension."
+        "symfony/dependency-injection": "^4.3|^5 If you'd like to use async event dispatcher container extension."
     },
     "autoload": {
         "psr-4": { "Enqueue\\AsyncCommand\\": "" },