Fix typo in chapter 10

Author: AriAbr

chapter_making_deployment_production_ready.asciidoc

@@ -438,7 +438,7 @@ _settings.py_ that we want to change for production:
   leaving those pages full of tracebacks available to the world
   https://docs.djangoproject.com/en/1.11/ref/settings/#debug[isn't secure].
 
-* `SECRET_KEY` is used by Django uses for some of its crypto--things like cookies
+* `SECRET_KEY` is used by Django for some of its crypto--things like cookies
   and CSRF protection. It's good practice to make sure the secret key on the
   server is different from the one in your source code repo, because that code
   might be visible to strangers.  We'll want to generate a new, random one but