brew-pull-circle.rb: Fix folder creation
brew-pull-circle.rb: Fix folder creation

Fixes:
 /tmp/brew/bin/brew [ 'pull-circle',
'--ci-upload',
'--keep-old',
'https://github.com/Linuxbrew/homebrew-core/pull/8436' ] ==> homebrew/core#8436
https://circleci.com/api/v1.1/project/github/Linuxbrew/homebrew-core/latest/artifacts?branch=pull/8436
Error: No such file or directory @ dir_s_mkdir - homebrew/core/8436

Closes Linuxbrew/homebrew-developer#84.

Signed-off-by: Michka Popoff <7b0496f66f66ee22a38826c310c38b415671b832@gmail.com>

Linuxbrew/homebrew-developer