Fix mongodb name in cron.json

There is a typo in cron.json making cron to fail
when mongodb is enabled.
Only affect master.

```MissingRequiredSource:
/var/lib/kolla/config_files/logrotate/mongdb.conf file is not found```

Change-Id: I79d41e94ee3361f2b4d831d17b1bb34a1964f580

ansible/roles/common/templates/cron.json.j2

@@ -31,7 +31,7 @@
     ( 'manila', enable_manila ),
     ( 'mariadb', enable_mariadb ),
     ( 'mistral', enable_mistral ),
-    ( 'mongdb', enable_mongodb ),
+    ( 'mongodb', enable_mongodb ),
     ( 'murano', enable_murano ),
     ( 'neutron', enable_neutron ),
     ( 'nova', enable_nova ),