Invert parity of env variable, now `ENABLE_DO_BY`

DoBy now won't run unless the variable is set. This fixes #2.
Merge pull request #6 from joallard/patch-1

Invert parity of env variable `DISABLE_DO_BY`
Add latest .ruby-version
Merge pull request #8 from padi/add_ruby_version

Add latest .ruby-version