Add PHP requirements

Nyholm · web-flow · commit 9027dda36fa9 · 2017-07-10T13:17:11.000+02:00
diff --git a/composer.json b/composer.json
@@ -14,7 +14,8 @@
         }
     },
     "require": {
-        "amphp/artax": "^3",
+        "php": "^7.0",
+        "amphp/artax": "^3.0",
         "php-http/httplug": "^1.1",
         "php-http/discovery": "^1.2"
     },
