Update file list for gemspec

Author: hsbt

fcntl.gemspec

@@ -11,12 +11,11 @@ Gem::Specification.new do |spec|
   spec.homepage      = "https://github.com/ruby/fcntl"
   spec.license       = "BSD-2-Clause"
 
-  spec.files         = `git ls-files -z`.split("\x0").reject do |f|
-    f.match(%r{^(test|spec|features)/})
-  end
+  spec.files         = ["ext/fcntl/extconf.rb", "ext/fcntl/fcntl.c"]
   spec.bindir        = "exe"
   spec.executables   = spec.files.grep(%r{^exe/}) { |f| File.basename(f) }
   spec.require_paths = ["lib"]
+  spec.extensions    = "ext/fcntl/extconf.rb"
   spec.required_ruby_version = ">= 2.5.0dev"
 
   spec.add_development_dependency "bundler", "~> 1.14"