* lib/rubygems.rb, lib/rubygems/*, test/rubygems/*: Update rubygems-2.5.2.

It supports to enable frozen string literal and add `--norc` option for
  disable to `.gemrc` configuration.
  See 2.5.2 release notes for other fixes and enhancements.
  a8aa3bac72/History.txt (L3)

git-svn-id: svn+ssh://ci.ruby-lang.org/ruby/trunk@53707 b2dd03c8-39d4-4d8f-98ff-823fe69b080e

lib/rubygems/resolver/activation_request.rb

@@ -1,4 +1,4 @@
-# frozen_string_literal: false
+# frozen_string_literal: true
 ##
 # Specifies a Specification object that should be activated.  Also contains a
 # dependency that was used to introduce this activation.
@@ -50,15 +50,27 @@ class Gem::Resolver::ActivationRequest
   # Downloads a gem at +path+ and returns the file path.
 
   def download path
-    if @spec.respond_to? :source
-      source = @spec.source
-    else
-      source = Gem.sources.first
-    end
-
     Gem.ensure_gem_subdirectories path
 
-    source.download full_spec, path
+    if @spec.respond_to? :sources
+      exception = nil
+      path = @spec.sources.find{ |source|
+        begin
+          source.download full_spec, path
+        rescue exception
+        end
+      }
+      return path      if path
+      raise  exception if exception
+
+    elsif @spec.respond_to? :source
+      source = @spec.source
+      source.download full_spec, path
+
+    else
+      source = Gem.sources.first
+      source.download full_spec, path
+    end
   end
 
   ##