therubyracer不在Windows上安装

当试图安装gem，我得到以下错误

C:\xampp\htdocs\mg>gem install therubyracer Temporarily enhancing PATH to include DevKit... Building native extensions. This could take a while... ERROR: Error installing therubyracer: ERROR: Failed to build gem native extension. C:/RailsInstaller/Ruby2.1.0/bin/ruby.exe -r ./siteconf20150527-5032-1urwkwd. rb extconf.rb creating Makefile The system cannot find the path specified. The system cannot find the path specified. The system cannot find the path specified. C:/RailsInstaller/Ruby2.1.0/lib/ruby/gems/2.1.0/gems/libv8-3.16.14.7/ext/libv8/b uilder.rb:68:in `setup_python!': libv8 requires python 2 to be installed in orde r to build, but it is currently not available (RuntimeError) from C:/RailsInstaller/Ruby2.1.0/lib/ruby/gems/2.1.0/gems/libv8-3.16.14. 7/ext/libv8/builder.rb:52:in `block in build_libv8!' from C:/RailsInstaller/Ruby2.1.0/lib/ruby/gems/2.1.0/gems/libv8-3.16.14. 7/ext/libv8/builder.rb:49:in `chdir' from C:/RailsInstaller/Ruby2.1.0/lib/ruby/gems/2.1.0/gems/libv8-3.16.14. 7/ext/libv8/builder.rb:49:in `build_libv8!' from C:/RailsInstaller/Ruby2.1.0/lib/ruby/gems/2.1.0/gems/libv8-3.16.14. 7/ext/libv8/location.rb:24:in `install!' from extconf.rb:7:in `<main>' extconf failed, exit code 1 Gem files will remain installed in C:/RailsInstaller/Ruby2.1.0/lib/ruby/gems/2.1 .0/gems/libv8-3.16.14.7 for inspection. Results logged to C:/RailsInstaller/Ruby2.1.0/lib/ruby/gems/2.1.0/extensions/x86 -mingw32/2.1.0/libv8-3.16.14.7/gem_make.out 

我已经尝试在Gemfile中添加这个

 gem 'therubyracer', gem 'less-rails 

试着

 gem uninstall libv8 gem install therubyracer -v=0.10.1 

以上一切失败，therubyracer从未安装。