Fix gemspec files

Author: jhawthorn

rapidjson.gemspec

@@ -21,9 +21,15 @@ Gem::Specification.new do |spec|
   # 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(File.expand_path(__dir__)) do
-    `git ls-files -z`.split("\x0").reject do |f|
-      (f == __FILE__) || f.match(%r{\A(?:(?:test|spec|features)/|\.(?:git|travis|circleci)|appveyor)})
-    end
+    [
+      Dir["ext/rapidjson/*.{hh,cc}"],
+      Dir["ext/rapidjson/rapidjson/include/**/*.h"],
+      Dir["lib/**/*.rb"],
+      "CODE_OF_CONDUCT.md",
+      "LICENSE.txt",
+      "README.md",
+      "Rakefile",
+    ].flatten
   end
   spec.bindir = "exe"
   spec.executables = spec.files.grep(%r{\Aexe/}) { |f| File.basename(f) }