Update podspec

Author: inamiy

SwiftTask.podspec

@@ -1,6 +1,6 @@
 Pod::Spec.new do |s|
   s.name     = 'SwiftTask'
-  s.version  = '4.2.0'
+  s.version  = '4.2.1'
   s.license  = { :type => 'MIT' }
   s.homepage = 'https://github.com/ReactKit/SwiftTask'
   s.authors  = { 'Yasuhiro Inami' => '[email protected]' }
@@ -13,4 +13,4 @@ Pod::Spec.new do |s|
   s.ios.deployment_target = '8.0'
   s.watchos.deployment_target = '2.0'
   s.tvos.deployment_target = '9.0'
-end
+end