Exclude PHP 8 and above as the code is not compatible

Author: duboism

composer.json

@@ -23,6 +23,7 @@
     },
     "type": "library",
     "require": {
+        "php": ">=5.6, < 8.0",
         "pear/pear_exception": "*",
         "pear/image_color": "*"
     }