tweaked gemspec file list

skyfall.gemspec

@@ -20,12 +20,8 @@ Gem::Specification.new do |spec|
   # spec.metadata["source_code_uri"] = "TODO: Put your gem's public repo URL here."
   # spec.metadata["changelog_uri"] = "TODO: Put your gem's CHANGELOG.md URL here."
 
-  # Specify which files should be added to the gem when it is released.
-  # The `git ls-files -z` loads the files in the RubyGem that have been added into git.
   spec.files = Dir.chdir(__dir__) do
-    `git ls-files -z`.split("\x0").reject do |f|
-      (File.expand_path(f) == __FILE__) || f.start_with?(*%w[bin/ test/ spec/ features/ .git .circleci appveyor])
-    end
+    Dir['*.md'] + Dir['*.txt'] + Dir['lib/**/*'] + Dir['sig/**/*']
   end
 
   spec.require_paths = ["lib"]