fix cocoapods link

Author: dakeshi

README.md

@@ -8,7 +8,7 @@ FirebaseUI clients are also available for [Android](https://github.com/firebase/
 
 ## Installing FirebaseUI for iOS
 
-FirebaseUI supports iOS 8.0+. We recommend using [CocoaPods](http://cocoapods.org/?q=firebaseui), add
+FirebaseUI supports iOS 8.0+. We recommend using [CocoaPods](https://cocoapods.org/pods/FirebaseUI), add
 the following to your `Podfile`:
 
 ```ruby