Update class-dump to v3.5

A new version of class-dump has been released and [`class-dump.rb`](https://github.com/mxcl/homebrew/blob/master/Library/Formula/class-dump.rb) needs updating.
It should be a simple task, but I'm unsure of one thing: The requirement of 10.9 SDK.

The [class-dump homepage](http://stevenygard.com/projects/class-dump/) says that it requires 10.8, which is fine if we downloaded the binary version and installed that.
But as of #22818 and 880d7cab34cc95abeaee4031aaa03fe76cbb986b we are compiling it with `xcodebuild`.

In the [release notes for class-dump 3.5](http://stevenygard.com/projects/class-dump/changes/), it is mentioned that it needs the 10.9 SDK to build, and I'm not sure how you'd like it to be done.