Update testing-ios.md

Author: BytesGuy

jekyll/_cci2/testing-ios.md

@@ -371,6 +371,8 @@ sudo gem install cocoapods
 
 We also recommend that you check your [Pods directory into source control](http://guides.cocoapods.org/using/using-cocoapods.html#should-i-check-the-pods-directory-into-source-control). This will ensure that you have a deterministic, reproducible build.
 
+**Note:** The previous S3 mirror we provided for the Cocoapods Spec repo is no longer being maintained or updated since the release of Cocoapods 1.8. It will remain available to prevent existing jobs breaking, we highly recommend switching to the CDN method described above. 
+
 ### Optimizing Homebrew
 {:.no_toc}