Updated link to Microsoft SQL Server backend.

docs/ref/databases.txt

@@ -1126,4 +1126,4 @@ the support channels provided by each 3rd party project.
 .. _CockroachDB: https://pypi.org/project/django-cockroachdb/
 .. _Firebird: https://pypi.org/project/django-firebird/
 .. _Google Cloud Spanner: https://pypi.org/project/django-google-spanner/
-.. _Microsoft SQL Server: https://pypi.org/project/django-mssql-backend/
+.. _Microsoft SQL Server: https://pypi.org/project/mssql-django/