Remove deprecated gemspec option

paperclip.gemspec

@@ -9,7 +9,6 @@ Gem::Specification.new do |s|
   s.email = %q{jyurek@thoughtbot.com}
   s.extra_rdoc_files = ["README.rdoc"]
   s.files = `git ls-files -z`.split("\x0").reject { |f| f.match(%r{^(test|gemfiles)/}) }
-  s.has_rdoc = true
   s.homepage = %q{http://www.thoughtbot.com/projects/paperclip}
   s.rdoc_options = ["--line-numbers", "--inline-source"]
   s.require_paths = ["lib"]