Test more recent ruby, remove EOL rubies

Author: SidOfc

.travis.yml

@@ -2,12 +2,10 @@ sudo: false
 language: ruby
 cache: bundler
 rvm:
- - 2.0.0
- - 2.1.0
  - 2.2.0
  - 2.3.0
  - 2.4.0
  - 2.5.0
-before_install: gem update bundler
+ - head
 script:
  - bundle exec rspec spec