Fixes composer setup

Author: moay

composer.json

@@ -8,9 +8,10 @@
         "guzzlehttp/guzzle": "^6.3"
     },
     "require-dev": {
-        "phpunit/phpunit": "^8.2"
+        "phpunit/phpunit": "^7"
     },
     "license": "MIT",
+    "minimum-stability": "stable",
     "authors": [
         {
             "name": "moay",