Installation Bundler找不到gem的兼容版本；actionpack“；安装gems时

在haml、引导sass和simple\u form gems上运行bundle install时，我得到以下信息：

Bundler could not find compatible versions for gem "actionpack":

rails (~> 5.1.0) was resolved to 5.1.0, which depends on
  actionpack (= 5.1.0)

rails (~> 5.1.0) was resolved to 5.1.0, which depends on
  actionpack (= 5.1.0)

rails (~> 5.1.0) was resolved to 5.1.0, which depends on
  actionpack (= 5.1.0)

simple_form (~> 3.0.2) was resolved to 3.0.2, which depends on
  actionpack (~> 4.0)

source 'https://rubygems.org'

gem 'rails', '~> 5.1.0'

gem 'haml', '~> 4.0.5'
gem 'simple_form', '~> 3.0.2'
gem 'bootstrap-sass', '~> 3.2.0.2'

我的文件如下所示：

Bundler could not find compatible versions for gem "actionpack":

rails (~> 5.1.0) was resolved to 5.1.0, which depends on
  actionpack (= 5.1.0)

rails (~> 5.1.0) was resolved to 5.1.0, which depends on
  actionpack (= 5.1.0)

rails (~> 5.1.0) was resolved to 5.1.0, which depends on
  actionpack (= 5.1.0)

simple_form (~> 3.0.2) was resolved to 3.0.2, which depends on
  actionpack (~> 4.0)

source 'https://rubygems.org'

gem 'rails', '~> 5.1.0'

gem 'haml', '~> 4.0.5'
gem 'simple_form', '~> 3.0.2'
gem 'bootstrap-sass', '~> 3.2.0.2'

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谁能告诉我哪里出了问题吗？thnx

我找到了这个并成功安装了它：

这：

即：