Update promise dependency

Author: sagikazarmark

composer.json

@@ -17,7 +17,7 @@
     "require": {
         "php": ">=5.4",
         "psr/http-message": "^1.0",
-        "php-http/promise": "^0.1"
+        "php-http/promise": "^1.0"
     },
     "require-dev": {
         "phpspec/phpspec": "^2.4",
@@ -36,5 +36,7 @@
         "branch-alias": {
             "dev-master": "1.0-dev"
         }
-    }
+    },
+    "prefer-stable": true,
+    "minimum-stability": "rc"
 }