Bump version to 3.3.1

Gifu.podspec

@@ -1,6 +1,6 @@
 Pod::Spec.new do |s|
   s.name = "Gifu"
-  s.version = "3.3"
+  s.version = "3.3.1"
   s.summary = "High-performance animated GIF support for iOS "
   s.homepage = "https://github.com/kaishin/Gifu"
   s.social_media_url = "http://twitter.com/kaishin"
@@ -9,7 +9,7 @@ Pod::Spec.new do |s|
   s.source = { :git => "https://github.com/kaishin/Gifu.git", :tag => "v#{s.version}", :submodules => true }
   s.platform = :ios, "9.0"
   s.platform = :tvos, "9.0"
-  s.swift_versions = ["5.0", "5.1", "5.2", "5.3"]
+  s.swift_versions = ["5.0", "5.1", "5.2", "5.3", "5.4"]
   s.ios.source_files = "Sources/**/*.{h,swift}"
   s.tvos.source_files = "Sources/**/*.{h,swift}"
   s.ios.deployment_target = "9.0"