Revert "Merge pull request #531 from stepanstipl/fix-gnu_sed"

This reverts commit 4de4bf9a0ac5a65ffc107102e7df5e124558955f, reversing
changes made to 9adae9897db20f0770e57cf3ba3f69c56662664d.

This broke Mac OS X sed
Merge branch 'master' of https://github.com/boxen/our-boxen