update dependencies

Author: hotrush

composer.json

@@ -10,15 +10,15 @@
         }
     ],
     "require": {
-        "php": ">=5.6.0",
+        "php": ">=7.1",
         "react/dns": "0.4.*",
-        "react/event-loop": "0.4.*",
-        "react/http-client": "0.4.*",
-        "react/http": "0.4.*",
-        "react/promise": "~2.1"
+        "react/event-loop": "0.5.*",
+        "react/http-client": "0.5.*",
+        "react/http": "0.8.*",
+        "react/promise": "~2.5"
     },
     "require-dev": {
-        "phpunit/phpunit": "^4.0|^5.0"
+        "phpunit/phpunit": "^6.0"
     },
     "autoload": {
         "psr-4": {