Add commented visionOS support for CocoaPods

Kingfisher.podspec

@@ -31,6 +31,8 @@ Pod::Spec.new do |s|
   s.tvos.deployment_target = "12.0"
   s.osx.deployment_target = "10.14"
   s.watchos.deployment_target = "5.0"
+  # Wait for CocoaPods 1.13.0 (visionOS support)
+  # s.visionos.deployment_target = "1.0"
 
   s.source       = { :git => "https://github.com/onevcat/Kingfisher.git", :tag => s.version }
   s.source_files  = ["Sources/**/*.swift"]