[refs tkadlec#20] Update URL for Instagram case study

_posts/2016-03-23-instagram-response-size.markdown

@@ -1,7 +1,7 @@
 ---
 layout: post
 title:  "Instagram increased impressions and user profile scroll interactions by decreasing the response size of the JSON needed for displaying comments (by 33% for the median and 50% for the 95th percentile for the main endpoint)."
-storySource: "http://engineering.instagram.com/posts/193415561023919/performance-&-usage-at-Instagram"
+storySource: "https://engineering.instagram.com/performance-usage-at-instagram-d2ba0347e442#.5snxp5z1t"
 date:   2016-03-23 11:27:51
 img:
  image: "instagram-logo.png"
@@ -10,4 +10,4 @@ tags:
  - engagement
  - impressions
  - "2016"
----
+---