Merge pull request doccano#423 from chakki-works/dependabot/pip/django-2.1.11

Bump django from 2.1.7 to 2.1.11

Author: Hironsan

requirements.txt

@@ -4,7 +4,7 @@ colour==0.1.5
 chardet==3.0.4
 coverage==4.5.3
 dj-database-url==0.5.0
-Django==2.1.7
+Django==2.1.11
 django-cloud-browser==0.5.0
 django-filter==2.0.0
 django-heroku==0.3.1