MPM-299 Allow php ^8.0 (#56)

* Allow php ^8.0

* Single pipe

* README changes

Co-authored-by: Marko <[email protected]>

Author: bajdzun

Diff for: README.md

@@ -15,7 +15,7 @@ The [documentation](https://arnaud.le-blanc.net/php-rdkafka/phpdoc/book.rdkafka.
 can help out to understand the internals of this library.
 
 ## Requirements
-- php: ^7.3
+- php: ^7.3|^8.0
 - ext-rdkafka: >=4.0.0
 - librdkafka: >=0.11.6 (if you use `<librdkafka:1.x` please define your own error callback)
 

Diff for: composer.json

@@ -17,7 +17,7 @@
     "rdkafka"
   ],
   "require": {
-    "php": "^7.3",
+    "php": "^7.3|^8.0",
     "ext-rdkafka": "^4.0|^5.0",
     "ext-json": "*"
   },