Add update migration for double dashes.

Library/Homebrew/cmd/update-report.rb

@@ -85,6 +85,7 @@ module Homebrew
     end
 
     migrate_legacy_cache_if_necessary
+    migrate_cache_entries_to_double_dashes
     migrate_legacy_keg_symlinks_if_necessary
 
     if !updated
@@ -183,6 +184,21 @@ module Homebrew
     end
   end
 
+  def migrate_cache_entries_to_double_dashes
+    HOMEBREW_CACHE.children.each do |child|
+      next unless child.file?
+
+      next unless /^(?<prefix>[^\.]+[^\-])\-(?<suffix>[^\-].*)/ =~ child.basename.to_s
+      target = HOMEBREW_CACHE/"#{prefix}--#{suffix}"
+
+      if target.exist?
+        FileUtils.rm_rf child
+      else
+        FileUtils.mv child, target, force: true
+      end
+    end
+  end
+
   def migrate_legacy_repository_if_necessary
     return unless HOMEBREW_PREFIX.to_s == "/usr/local"
     return unless HOMEBREW_REPOSITORY.to_s == "/usr/local"