mongodb26: 2.6.12
mongodb26: 2.6.12

Also includes macOS Sierra compatibility
Making requested changes and squashing commit

Hard coding values for accepted MacOS versions as requested

Closes #1411.

Signed-off-by: Mike McQuaid <a17fed27eaa842282862ff7c1b9c8395a26ac320@mikemcquaid.com>

coeligena/homebrew-verscustomized,heuermh/homebrew-versions