Changed supported version

Author: Andrey Helldar

composer.json

@@ -15,12 +15,12 @@
         }
     ],
     "require": {
-        "php": ">=5.6.9",
+        "php": "^7.1.3",
         "ext-json": "*",
-        "symfony/http-foundation": "^3.0|^4.0|^5.0"
+        "symfony/http-foundation": "^4.0|^5.0"
     },
     "require-dev": {
-        "phpunit/phpunit": "^6.5|^7.0"
+        "phpunit/phpunit": "^8.5"
     },
     "suggest": {
         "symfony/thanks": "Give thanks (in the form of a GitHub) to your fellow PHP package maintainers"