Storing item with Touch Id: Fixed case where we overwrite an existing entry with touch Id

SecItemUpdate(...) is not allowed on items with TouchId enabled.
See Known Issues: https://developer.apple.com/library/ios/releasenotes/General/RN-iOSSDK-8.0/
We now delete the old item and add a new one.
Fixed hasValueForKey method: Always returned NO as long as key was != null
Merge pull request #4 from ti8mag/master

Fixed issue with TouchId and hasValueForKey: