Fixup more frozen string handling.

Library/Homebrew/utils/inreplace.rb

@@ -3,10 +3,10 @@
 module Utils
   class InreplaceError < RuntimeError
     def initialize(errors)
-      formatted_errors = errors.reduce("inreplace failed\n") do |s, (path, errs)|
+      formatted_errors = errors.reduce(+"inreplace failed\n") do |s, (path, errs)|
         s << "#{path}:\n" << errs.map { |e| "  #{e}\n" }.join
       end
-      super formatted_errors
+      super formatted_errors.freeze
     end
   end