[Podspec] Remove circular dependency

You do not need to explicitly depend on a subspace since by default it will be included. The subspec will contain the dependency from it's parent spec and therefore lead to a circular dependency.

As noted in https://github.com/CocoaPods/Molinillo/issues/6, the coming version of CocoaPods will now allow this.
Merge pull request #3 from kylef/patch-1

[Podspec] Remove circular dependency