resolver.rb in rubygems-update-2.5.2

- old
+ new

@@ -1,5 +1,6 @@
+# frozen_string_literal: true
 require 'rubygems/dependency'
 require 'rubygems/exceptions'
 require 'rubygems/util'
 require 'rubygems/util/list'
 
@@ -276,9 +277,10 @@
 require 'rubygems/resolver/git_set'
 require 'rubygems/resolver/index_set'
 require 'rubygems/resolver/installer_set'
 require 'rubygems/resolver/lock_set'
 require 'rubygems/resolver/vendor_set'
+require 'rubygems/resolver/source_set'
 
 require 'rubygems/resolver/specification'
 require 'rubygems/resolver/spec_specification'
 require 'rubygems/resolver/api_specification'
 require 'rubygems/resolver/git_specification'