Use gem update --system to update rubygems on Windows

Previously, the student was required to download a package
and install it with `update_rubygems`

Fixes railsbridge#596

Author: tjgrathwell

lib/site_extensions/installfest.rb

@@ -6,8 +6,8 @@ def version_string(name)
           '2.3'
         when :windows_rubygems_min
           '2.6.7'
-        when :windows_rubygems_current
-          '2.6.8'
+        when :windows_rubygems_min_short
+          '2.6'
         else
           raise StandardError, "No version string exists for '#{name}'"
       end

sites/en/installfest/windows.step

@@ -83,36 +83,25 @@ step "Open a Terminal" do
 end
 
 step "Update RubyGems" do
-  message "The version of RubyGems that comes with RailsInstaller has some problems. Follow these steps to upgrade it!"
+  message "The version of RubyGems that comes with RailsInstaller may be outdated. Follow these steps to upgrade it!"
 
   step "Check to see if you need to update" do
     console "gem -v"
 
-    message "If the output is **2.6.6** or earlier, keep following the instructions."
-
     message "If the output is **#{version_string(:windows_rubygems_min)}** or later, <a href='#install-node'>skip to the next step!</a>"
   end
 
-  step "Download the update" do
-    message "Visit https://rubygems.org/downloads/rubygems-update-#{version_string(:windows_rubygems_current)}.gem"
-
-    message "**Right click -> Save target as...** the file **rubygems-update-#{version_string(:windows_rubygems_current)}.gem** to your **C:\\Sites** directory"
-  end
-
-  step "Install the update" do
-    message "Back at the command prompt, run the following commands:"
-
-    console_without_message "gem install --local C:\\Sites\\rubygems-update-#{version_string(:windows_rubygems_current)}.gem"
+  step "Install the latest version of RubyGems" do
+    message "Otherwise, run the following command:"
 
-    console_without_message "update_rubygems --no-document"
+    console_without_message "gem update --system --no-document"
 
     message "**Close and reopen your command prompt**, then verify you have the upgraded RubyGems by typing this in the terminal:"
 
     console_without_message "gem -v"
-    result version_string(:windows_rubygems_current)
+    fuzzy_result "#{version_string(:windows_rubygems_min_short)}{FUZZY}.9{/FUZZY}"
 
-    message "Finally, you can clean up by running the following command:"
-    console_without_message "gem uninstall rubygems-update -x"
+    message "As long as the version is at least **#{version_string(:windows_rubygems_min)}**, you should be fine!"
   end
 end