Adjust podspec for networking changes (#660)
Adjust podspec for networking changes (#660)

* Adjust podspec for networking changes
* Add default_subspec to avoid installing all three subspecs

BranchMetrics/iOS-Deferred-Deep-Linking-SDK,BranchMetrics/ios-branch-deep-linking,BranchMetrics/ios-branch-deep-linking,BranchMetrics/iOS-Deferred-Deep-Linking-SDK,BranchMetrics/ios-branch-deep-linking,BranchMetrics/ios-branch-deep-linking