[Podspec] Fix a typo causing a circular dependency

Discovered because of a circular dependency in the podspec via https://github.com/CocoaPods/Resolver/issues/6

Since the root spec is depending on the subspecs, the subspaces also depend on the root spec. Thus a circular dependency issue.
Merge pull request #4 from kylef/patch-1

[Podspec] Fix a typo causing a circular dependency