Drop PHP 7.2 support since myclabs/php-enum is now >=7.3

Author: phpfui

composer.json

@@ -13,7 +13,7 @@
         }
     ],
     "require": {
-        "php": ">=7.2",
+        "php": ">=7.3",
         "ext-mbstring": "*",
         "ext-zlib": "*",
         "ext-curl": "*",
@@ -25,7 +25,7 @@
         "psr/http-client": "^1.0"
     },
     "require-dev": {
-        "phpunit/phpunit": "^7.5.1 || ^8.0 || ^9.0",
+        "phpunit/phpunit": "^8.0 || ^9.0",
         "mockery/mockery": "^1.2",
         "friendsofphp/php-cs-fixer": "^3.0",
         "phan/phan": "^5.2"