Bump Symfony requirement to 4.4.X

As 5.X is the stable branch and 4.4 the LTS I've changed the requirements to make an update to the 4.X libraries we use easier.

This update should resolve the vulnerabilities in PR #2, #3, #4 and #5.

composer.json

@@ -6,12 +6,12 @@
         "ext-ctype": "*",
         "ext-iconv": "*",
         "nyholm/psr7": "^1.2",
-        "symfony/console": "^4.0",
-        "symfony/dotenv": "^4.0",
-        "symfony/expression-language": "^4.0",
+        "symfony/console": "~4.3",
+        "symfony/dotenv": "~4.3",
+        "symfony/expression-language": "~4.3",
         "symfony/flex": "^1.3.1",
-        "symfony/framework-bundle": "^4.0",
-        "symfony/yaml": "^4.0",
+        "symfony/framework-bundle": "~4.3",
+        "symfony/yaml": "~4.3",
         "trikoder/oauth2-bundle": "^2.0"
     },
     "require-dev": {
@@ -21,8 +21,8 @@
         "phpstan/phpstan": "^0.11.16",
         "roave/security-advisories": "dev-master",
         "squizlabs/php_codesniffer": "^3.5",
-        "symfony/var-dumper": "^4.0",
-        "symfony/web-server-bundle": "^4.0"
+        "symfony/var-dumper": "~4.3",
+        "symfony/web-server-bundle": "~4.3"
     },
     "config": {
         "preferred-install": {
@@ -66,7 +66,7 @@
     "extra": {
         "symfony": {
             "allow-contrib": false,
-            "require": "4.4.*"
+            "require": "~4.3"
         }
     }
 }