language: ruby
rvm:
  - 2.1
  - 2.2.10
  - 2.3.8
  - 2.4.5
  - 2.5.3
  - 2.6.0

language: ruby
rvm:
  - 2.3.8
  - 2.4.6
  - 2.5.7
  - 2.6.5

Drop support of old Rubies
Drop support of old Rubies

The minitest dropped the support of old Rubies(< 2.3) in 5.12.
I follow the same policy.
