Use Mac' codesign identities for OSX targets

I've faced with codesign errors while trying build with Carthage 0.3 like this:
```
=== BUILD TARGET SwiftyJSONOSX OF PROJECT SwiftyJSON WITH CONFIGURATION Release ===

Check dependencies
Code Sign error: Multiple matching codesigning identities found: Multiple codesigning identities (i.e. certificate and private key pairs) matching “iPhone Distribution” were found.
```
So, this PR will solve them.