[rubygems/rubygems] Move rubygems source specific logic to rubygems source

https://github.com/rubygems/rubygems/commit/6aa4c422a7

lib/bundler/runtime.rb

@@ -125,7 +125,6 @@ module Bundler
       specs_to_cache.each do |spec|
         next if spec.name == "bundler"
         next if spec.source.is_a?(Source::Gemspec)
-        spec.source.send(:fetch_gem, spec) if Bundler.settings[:cache_all_platforms] && spec.source.respond_to?(:fetch_gem, true)
         spec.source.cache(spec, custom_path) if spec.source.respond_to?(:cache)
       end
 

lib/bundler/source/rubygems.rb

@@ -242,7 +242,7 @@ module Bundler
       end
 
       def cache(spec, custom_path = nil)
-        cached_path = cached_gem(spec)
+        cached_path = Bundler.settings[:cache_all_platforms] ? fetch_gem(spec) : cached_gem(spec)
         raise GemNotFound, "Missing gem file '#{spec.file_name}'." unless cached_path
         return if File.dirname(cached_path) == Bundler.app_cache.to_s
         Bundler.ui.info "  * #{File.basename(cached_path)}"