use crawler only to register signals in from_crawler()

scrapy/templates/project/module/middlewares.py.tmpl

@@ -16,7 +16,7 @@ class ${ProjectName}SpiderMiddleware(object):
     @classmethod
     def from_crawler(cls, crawler):
         # This method is used by Scrapy to create your spiders.
-        s = cls(crawler.stats)
+        s = cls()
         crawler.signals.connect(s.spider_opened, signal=signals.spider_opened)
         return s