Update Objective-C examples

This was just a quick pass to update the objc examples with what I feel like we actually follow.

I removed the `enumerateObjectsUsingBlock:` portion too. Partially because I feel like that's not actually what we use, and then there's this: http://www.objc.io/issue-7/collections.html Either way I don't feel like we follow a hard and fast rule about that so that portion now just references the spacing.

// @thoughtbot/ios
Are we following this "use k as a prefix for key constants" thing? I'm not.