Correct naming file from Mingw

mrbgems/mruby-io/mrbgem.rake

@@ -6,9 +6,9 @@ MRuby::Gem::Specification.new('mruby-io') do |spec|
   spec.cc.include_paths << "#{build.root}/src"
 
   if for_windows?
-    spec.linker.libraries += ['Ws2_32']
+    spec.linker.libraries << "ws2_32"
     #spec.cc.include_paths += ["C:/Windows/system/include"]
-    spec.linker.library_paths += ["C:/Windows/system"]
+    spec.linker.library_paths << "C:/Windows/system"
   end
   spec.add_test_dependency 'mruby-time', core: 'mruby-time'
 end