Add actioncable assets to gemspec.

actioncable.js and actioncable.esm.js is not included to gem package. It prevented us from using the action cable when using importmaps.

This adds the missing asset files to gem package.

Author: ytnk531

actioncable/actioncable.gemspec

@@ -17,7 +17,7 @@ Gem::Specification.new do |s|
   s.email    = ["[email protected]", "[email protected]"]
   s.homepage = "https://rubyonrails.org"
 
-  s.files        = Dir["CHANGELOG.md", "MIT-LICENSE", "README.md", "lib/**/*", "app/assets/javascripts/action_cable.js"]
+  s.files        = Dir["CHANGELOG.md", "MIT-LICENSE", "README.md", "lib/**/*", "app/assets/javascripts/*.js"]
   s.require_path = "lib"
 
   s.metadata = {