Related to https://github.com/h2o/h2o/issues/2789

--- a/deps/mruby/Rakefile
+++ b/deps/mruby/Rakefile
@@ -37,15 +37,15 @@
 task :default => :all
 
 bin_path = ENV['INSTALL_DIR'] || "#{MRUBY_ROOT}/bin"
-FileUtils.mkdir_p bin_path, { :verbose => $verbose }
+FileUtils.mkdir_p bin_path, verbose: $verbose
 
 depfiles = MRuby.targets['host'].bins.map do |bin|
   install_path = MRuby.targets['host'].exefile("#{bin_path}/#{bin}")
   source_path = MRuby.targets['host'].exefile("#{MRuby.targets['host'].build_dir}/bin/#{bin}")
 
   file install_path => source_path do |t|
-    FileUtils.rm_f t.name, { :verbose => $verbose }
-    FileUtils.cp t.prerequisites.first, t.name, { :verbose => $verbose }
+    FileUtils.rm_f t.name, verbose: $verbose
+    FileUtils.cp t.prerequisites.first, t.name, verbose: $verbose
   end
 
   install_path
@@ -78,8 +78,8 @@
         install_path = MRuby.targets['host'].exefile("#{bin_path}/#{bin}")
 
         file install_path => exec do |t|
-          FileUtils.rm_f t.name, { :verbose => $verbose }
-          FileUtils.cp t.prerequisites.first, t.name, { :verbose => $verbose }
+          FileUtils.rm_f t.name, verbose: $verbose
+          FileUtils.cp t.prerequisites.first, t.name, verbose: $verbose
         end
         depfiles += [ install_path ]
       elsif target == MRuby.targets['host-debug']
@@ -87,8 +87,8 @@
           install_path = MRuby.targets['host-debug'].exefile("#{bin_path}/#{bin}")
 
           file install_path => exec do |t|
-            FileUtils.rm_f t.name, { :verbose => $verbose }
-            FileUtils.cp t.prerequisites.first, t.name, { :verbose => $verbose }
+            FileUtils.rm_f t.name, verbose: $verbose
+            FileUtils.cp t.prerequisites.first, t.name, verbose: $verbose
           end
           depfiles += [ install_path ]
         end
@@ -127,16 +127,16 @@
 desc "clean all built and in-repo installed artifacts"
 task :clean do
   MRuby.each_target do |t|
-    FileUtils.rm_rf t.build_dir, { :verbose => $verbose }
+    FileUtils.rm_rf t.build_dir, verbose: $verbose
   end
-  FileUtils.rm_f depfiles, { :verbose => $verbose }
+  FileUtils.rm_f depfiles, verbose: $verbose
   puts "Cleaned up target build folder"
 end
 
 desc "clean everything!"
 task :deep_clean => ["clean"] do
   MRuby.each_target do |t|
-    FileUtils.rm_rf t.gem_clone_dir, { :verbose => $verbose }
+    FileUtils.rm_rf t.gem_clone_dir, verbose: $verbose
   end
   puts "Cleaned up mrbgems build folder"
 end