Update composer.json

Author: Swader

composer.json

@@ -21,7 +21,7 @@
     "php": ">=5.4.0",
     "php-http/client-implementation": "^1.0",
     "php-http/utils": "dev-master",
-    "php-http/discovery": "^0.2.0@dev"
+    "php-http/discovery": "dev-master"
   },
   "require-dev": {
     "symfony/var-dumper": "~2",