ruby21 2.1.6
ruby21 2.1.6

Version bump to fix CVE-2015-1855.

Closes #768.

Signed-off-by: Dominyk Tiller <53e438f55903875d07efdd98a8aaf887e7208dd3@gmail.com>

jimhe/homebrew-versions,coeligena/homebrew-verscustomized,UniqMartin/homebrew-versions,heuermh/homebrew-versions,DomT4/homebrew-versions,Ashton-W/homebrew-versions