Make sure redirected stdout and stderr share the same offset

This fixes broken output like this:

  Error: No such file or directory - non_existent_file
  ee/src/tree-1.7.0.tgz
  Already downloaded: /Library/Caches/Homebrew/tree-1.7.0.tgz
  ==> Verifying tree-1.7.0.tgz checksum
  tar xf /Library/Caches/Homebrew/tree-1.7.0.tgz