title: Rails install fails: activesupport requires Ruby version >= 2.2.2
body: <p>I want to create a new Rails app. I am using rvm with ruby-2.1.2. I am usint the <code>@global</code> gemset and plan to use bundler to manage gem dependencies. However, <code>gem install rails</code> fails:</p>
  
  <pre><code>$ gem install rails
  Fetching: concurrent-ruby-1.0.3.pre3.gem (100%)
  Successfully installed concurrent-ruby-1.0.3.pre3
  Fetching: minitest-5.9.0.gem (100%)
  Successfully installed minitest-5.9.0
  Fetching: thread_safe-0.3.5.gem (100%)
  Successfully installed thread_safe-0.3.5
  Fetching: tzinfo-1.2.2.gem (100%)
  Successfully installed tzinfo-1.2.2
  Fetching: i18n-0.7.0.gem (100%)
  Successfully installed i18n-0.7.0
  Fetching: activesupport-5.0.0.gem (100%)
  ERROR:  Error installing rails:
      activesupport requires Ruby version &gt;= 2.2.2.
  </code></pre>
  
  <p>Yes, it is true I am using ruby-2.1.2 and not ruby-2.2.2, but shouldn't I still be allowed to use ruby-2.1.2? Are we not allowed to use ruby-2.1.2 anymore?</p>
  
  <p>I thought maybe that ActiveSupport 5 was already installed in the <code>@global</code> gemset and that ActiveSupport 5 required 2.2.2, but actually there is no ActiveSupport 5 in the <code>@global</code> gemset:</p>
  
  <pre><code>$ rvm gemdir
  /Users/myuser/.rvm/gems/ruby-2.1.2@global
  $ cd /Users/myuser/.rvm/gems/ruby-2.1.2@global
  $ cd gems
  $ ls
  bundler-unload-1.0.2        gem-wrappers-1.2.4      rake-10.1.0         rvm-1.11.3.9            tzinfo-1.2.2
  concurrent-ruby-1.0.3.pre3  i18n-0.7.0          rdoc-4.1.0          test-unit-2.1.2.0
  executable-hooks-1.3.2      minitest-5.9.0          rubygems-bundler-1.4.4      thread_safe-0.3.5
  </code></pre>
  
  <p>So how can I prevent this error from occurring while trying to use ruby-2.1.2?</p>