CLC-3551 /api/blog should update the alert field every 2 minutes

https://jira.ets.berkeley.edu/jira/browse/CLC-3551

Summary: The call to /api/blog should update the "alert" field every 2 minutes. The latest releases part (entries) refreshes at the default rate of 35 minutes.

Jira notes:
On the Splash page, the alert field of the /api/blog feed should be updated every two minutes. 

How to reproduce: 
1. Go to the Calcentral splash page 
2. Load /api/blog, and notice the alert field 
3. Go to Drupal and change the alert information 
4. Wait for two minutes and clean your fingernails 
5. Reload the splash page or /api/blog 

Current behavior: 
The alert message is not being updated every 2 minutes 

Expected behavior: 
We expect to see the alert message updasted every two minutes 

Notes:
Removed the following line from the BlogFeedController:
 - caches_action(:get_latest_release_notes, :expires_in => EtsBlog::ReleaseNotes.expires_in)
EtsBlog::ReleaseNotes::get_latest_release_notes is already being cached with the default expiration time.