Added Base64 dependency for NSString subspec.
Added Base64 dependency for NSString subspec.

michalkonturek/MKFoundationKit,Thesaurus/MKFoundationKit,Thesaurus/MKFoundationKit,Thesaurus/MKFoundationKit,michalkonturek/MKFoundationKit,michalkonturek/MKFoundationKit,michalkonturek/MKFoundationKit,Thesaurus/MKFoundationKit