Fix bug for ".local" host name

It's necessary to put new list member in squared brackets (i.e. create new list) to merge lists properly, otherwise we will get result list with character elements instead of string element.

scrapy/http/cookies.py

@@ -29,7 +29,7 @@ class CookieJar(object):
         if not IPV4_RE.search(req_host):
             hosts = potential_domain_matches(req_host)
             if req_host.find(".") == -1:
-                hosts += req_host + ".local"
+                hosts += [req_host + ".local"]
         else:
             hosts = [req_host]