[ruby/fcntl] Fixup gemspec files

https://github.com/ruby/fcntl/commit/9e14019f53

ext/fcntl/fcntl.gemspec

@@ -23,7 +23,7 @@ Gem::Specification.new do |spec|
   spec.licenses      = ["Ruby", "BSD-2-Clause"]
 
   spec.files         = ["ext/fcntl/extconf.rb", "ext/fcntl/fcntl.c"]
-  spec.extra_rdoc_files = [".document", ".rdoc_options", "LICENSE.txt", "README.md"]
+  spec.extra_rdoc_files = [".document", ".rdoc_options", "BSDL", "COPYING", "README.md"]
   spec.bindir        = "exe"
   spec.executables   = spec.files.grep(%r{^exe/}) { |f| File.basename(f) }
   spec.require_paths = ["lib"]