[ruby/rubygems] Deprecate --default option

https://github.com/ruby/rubygems/commit/55745ee0f8

lib/rubygems/install_update_options.rb

@@ -158,7 +158,7 @@ module Gem::InstallUpdateOptions
       options[:without_groups].concat v.map(&:intern)
     end
 
-    add_option(:"Install/Update", "--default",
+    add_option(:Deprecated, "--default",
                "Add the gem's full specification to",
                "specifications/default and extract only its bin") do |v,_o|
       options[:install_as_default] = v