Temporary sandbox directories not cleaned up after run

[RSTJNII]

Per the documentation Strainer is supposed to clean up temporary directories by relying on Dir.mktmpdir. However, this is not happening with Strainer 3.3.0. The behavior appears to be due to the usage of Dir.mktmpdir. Strainer is calling Dir.mktmpdir with no arguments:

$ grep Dir.mktmpdir lib/strainer.rb 
      @sandbox_path ||= Pathname.new(Dir.mktmpdir)
      @logfile_path ||= Pathname.new(File.join(Dir.mktmpdir, 'strainer.out'))

However, per the Ruby 1.9.3 docs Dir.mktmpdir doesn't clean up after itself when called this way:

If a block is not given, The path of the directory is returned. In this case, ::mktmpdir doesn’t remove the directory.