adjust composer.json

Author: nick-zh

composer.json

@@ -2,7 +2,7 @@
   "name": "widmogrod/php-functional",
   "description": "Functors, Applicative and Monads are fascinating concept. Purpose of this library is to explore them in OOP PHP world.",
   "require": {
-    "php": ">=7.1",
+    "php": "^7.1|^8.0",
     "functional-php/fantasy-land": "^1"
   },
   "require-dev": {