[ruby/optparse] Fix typo [ci skip]

https://github.com/ruby/optparse/commit/0aec9adfc5

lib/optparse/optparse.gemspec

@@ -23,7 +23,7 @@ Gem::Specification.new do |spec|
   spec.metadata["source_code_uri"] = spec.homepage
 
   spec.files         = Dir["{doc,lib,misc}/**/{*,.document}"] +
-                       %w[README.md ChangeLog COPYING .document .rdoc_options"]
+                       %w[README.md ChangeLog COPYING .document .rdoc_options]
   spec.rdoc_options  = ["--main=README.md", "--op=rdoc", "--page-dir=doc"]
   spec.bindir        = "exe"
   spec.executables   = []