[Objective-C] Fixes a broken link

This got changed recently.

Objective-C.gitignore

@@ -21,6 +21,6 @@ DerivedData
 #
 # We recommend against adding the Pods directory to your .gitignore. However
 # you should judge for yourself, the pros and cons are mentioned at:
-# http://guides.cocoapods.org/using/using-cocoapods.html#should-i-ignore-the-pods-directory-in-source-control?
+# http://guides.cocoapods.org/using/using-cocoapods.html#should-i-ignore-the-pods-directory-in-source-control
 #
 # Pods/