Forward compatibility with ChildProcess v0.6

Author: clue

composer.json

@@ -12,7 +12,7 @@
     ],
     "require": {
         "php": ">=5.3",
-        "react/child-process": "^0.5 || ^0.4 || ^0.3",
+        "react/child-process": "^0.6 || ^0.5 || ^0.4 || ^0.3",
         "react/event-loop": "^1.0 || ^0.5 || ^0.4 || ^0.3",
         "react/promise": "~2.0|~1.0"
     },