Upgrade ruby to 2.7.6

[sau226]

We are currently running ruby 2.7.6 on our dev server. Currently, the auto-deploy job in CircleCI is failing because a ruby version mismatch error is thrown after git operations occur, as this repo expects ruby 2.6.6 to be running.

As dev has been moving along just fine with this bump, this PR goes ahead and upgrades ruby from 2.6.6 to 2.7.6. An upgrade of the ruby version on prod will need to occur before this deploys.