Forward compatibility with react/promise 3

Author: WyriHaximus

composer.json

@@ -20,7 +20,7 @@
     "require": {
         "php": ">=5.3",
         "react/event-loop": "^1.0 || ^0.5 || ^0.4 || ^0.3.5",
-        "react/promise": "^2.7.0 || ^1.2.1"
+        "react/promise": "dev-master as 3.0.0 || ^2.7.0 || ^1.2.1"
     },
     "require-dev": {
         "phpunit/phpunit": "^6.4 || ^5.7 || ^4.8.35"