Fixed PodSpec for tvOS (#140)

Fixed PodSpec for tvOS
diff --git a/GoogleToolboxForMac.podspec b/GoogleToolboxForMac.podspec
index b4bf22b..452679a 100644
--- a/GoogleToolboxForMac.podspec
+++ b/GoogleToolboxForMac.podspec
@@ -36,8 +36,7 @@
     sp.frameworks = 'AddressBook'
     sp.dependency 'GoogleToolboxForMac/Core', "#{s.version}"
     sp.dependency 'GoogleToolboxForMac/Defines', "#{s.version}"
-    sp.platform = :ios
-    sp.platform = :osx
+    sp.platforms = { :ios => '5.0', :osx => '10.6' }
   end
 
   s.subspec 'DebugUtils' do |sp|