add watchos target

CryptoSwift.podspec

@@ -12,6 +12,8 @@ Pod::Spec.new do |s|
   s.ios.deployment_target = "8.0"
   s.osx.platform  = :osx, '10.9'
   s.osx.deployment_target = "10.9"
+  s.watchos.platform = :watchos, '2.0'
+  s.watchos.deployment_target = "2.0"
   s.source_files  = "CryptoSwift/*.swift"
   s.requires_arc = true
 end