after ruby-2.6.0, set Net::HTTP#write_timeout

Author: thekuwayama

test/webrick/test_filehandler.rb

@@ -308,7 +308,7 @@ def req.meta_vars
     TestWEBrick.start_httpserver(config, log_tester) do |server, addr, port, log|
       http = Net::HTTP.new(addr, port)
       http.read_timeout = EnvUtil.apply_timeout_scale(60)
-      http.write_timeout = EnvUtil.apply_timeout_scale(60)
+      http.write_timeout = EnvUtil.apply_timeout_scale(60) if Gem::Version.new(RUBY_VERSION) >= Gem::Version.new('2.6.0')
 
       req = Net::HTTP::Get.new("/webrick.cgi/test")
       http.request(req) do |res|