Link to codebase of example app, rather than server instance (#879)

get_started/tutorial_multi_tenant.rst

@@ -16,7 +16,7 @@ Data model and sample data
 ---------------------------
 
 We will demo building the database for an ad-analytics app which companies can use to view, change,
-analyze and manage their ads and campaigns (see an `example app <http://citus-example-ad-analytics.herokuapp.com/>`_).
+analyze and manage their ads and campaigns (see an `example app <https://github.com/citusdata/citus-example-ad-analytics/>`_).
 Such an application has good characteristics of a typical multi-tenant system. Data from different tenants is stored in a central database, and each tenant has an isolated view of their own data.
 
 We will use three Postgres tables to represent this data. To get started, you will need to download sample data for these tables: