Revert "Update DifferentiationSNP.Rmd"
Revert "Update DifferentiationSNP.Rmd"

This reverts commit d5ca1b8ce9911e33382832bf3fde89f8a16c8ad7. The commit
was breaking the build, which we should avoid as much as possible on the
master branch.

NESCent/popgenInfo,bjcochrane/popgenInfo