安装ruby rest-client时出现问题

Question

我最近尝试在Ruby上安装rest-client，以便跟随教程，我收到错误，我将在下面发布。我已经成功安装了DevKit。当我输入gem -v时，命令提示符返回2.2.5。整个错误都在下面。

Gem files will remain installed in C:/Ruby21/lib/ruby/gems/2.1.0/gems/unf-0.2.0.
beta2/ext/gems/gems/unf_ext-0.0.7.1 for inspection.
Results logged to C:/Ruby21/lib/ruby/gems/2.1.0/gems/unf-0.2.0.beta2/ext/gems/ex
tensions/x86-mingw32/2.1.0/unf_ext-0.0.7.1/gem_make.out
        from C:/Ruby21/lib/ruby/2.1.0/rubygems/ext/ext_conf_builder.rb:38:in `bl
ock in build'
        from C:/Ruby21/lib/ruby/2.1.0/tempfile.rb:324:in `open'
        from C:/Ruby21/lib/ruby/2.1.0/rubygems/ext/ext_conf_builder.rb:17:in `bu
ild'
        from C:/Ruby21/lib/ruby/2.1.0/rubygems/ext/builder.rb:161:in `block (2 l
evels) in build_extension'
        from C:/Ruby21/lib/ruby/2.1.0/rubygems/ext/builder.rb:160:in `chdir'
        from C:/Ruby21/lib/ruby/2.1.0/rubygems/ext/builder.rb:160:in `block in b
uild_extension'
        from C:/Ruby21/lib/ruby/2.1.0/rubygems/ext/builder.rb:159:in `synchroniz
e'
        from C:/Ruby21/lib/ruby/2.1.0/rubygems/ext/builder.rb:159:in `build_exte
nsion'
        from C:/Ruby21/lib/ruby/2.1.0/rubygems/ext/builder.rb:198:in `block in b
uild_extensions'
        from C:/Ruby21/lib/ruby/2.1.0/rubygems/ext/builder.rb:195:in `each'
        from C:/Ruby21/lib/ruby/2.1.0/rubygems/ext/builder.rb:195:in `build_exte
nsions'
        from C:/Ruby21/lib/ruby/2.1.0/rubygems/installer.rb:677:in `build_extens
ions'
        from C:/Ruby21/lib/ruby/2.1.0/rubygems/installer.rb:232:in `install'
        from C:/Ruby21/lib/ruby/2.1.0/rubygems/resolver/specification.rb:78:in `
install'
        from C:/Ruby21/lib/ruby/2.1.0/rubygems/request_set.rb:206:in `block in i
nstall_into'
        from C:/Ruby21/lib/ruby/2.1.0/rubygems/request_set.rb:198:in `each'
        from C:/Ruby21/lib/ruby/2.1.0/rubygems/request_set.rb:198:in `install_in
to'
        from C:/Ruby21/lib/ruby/2.1.0/rubygems/request_set.rb:119:in `install'
        from C:/Ruby21/lib/ruby/2.1.0/rubygems/dependency_installer.rb:389:in `i
nstall'
        from mkrf_conf.rb:15:in `<main>'
Building native extensions.  This could take a while...

rake failed, exit code 1

Gem files will remain installed in C:/Ruby21/lib/ruby/gems/2.1.0/gems/unf-0.2.0.
beta2 for inspection.
Results logged to C:/Ruby21/lib/ruby/gems/2.1.0/extensions/x86-mingw32/2.1.0/unf
-0.2.0.beta2/gem_make.out