Fixed middleware syntax issue in Python 2.7

Author: syrusakbary

graphql/execution/middleware.py

@@ -10,9 +10,9 @@
 class MiddlewareManager(object):
     __slots__ = "middlewares", "wrap_in_promise", "_middleware_resolvers", "_cached_resolvers"
 
-    def __init__(self, *middlewares, wrap_in_promise=True):
+    def __init__(self, *middlewares, **kwargs):
         self.middlewares = middlewares
-        self.wrap_in_promise = wrap_in_promise
+        self.wrap_in_promise = kwargs.get('wrap_in_promise', True)
         self._middleware_resolvers = list(get_middleware_resolvers(middlewares)) if middlewares else []
         self._cached_resolvers = {}