DDOCSP-18787 update download links on index page 4.0

Author: ianf-mongodb

source/index.txt

@@ -12,7 +12,7 @@ The MongoDB |version| Manual
    For new features in MongoDB 4.0, see :doc:`/release-notes/4.0`.
 
    To download the MongoDB 4.0, go to the `MongoDB Download Center
-   <https://www.mongodb.com/download-center?jmp=docs#production>`_
+   <https://www.mongodb.com/try/download?tck=docs_server>`_
 
 
 .. include:: /includes/fact-mongodb-intro.rst