Update Travis config with new Ruby and Rails

Author: brateq

.travis.yml

@@ -1,10 +1,13 @@
 language: ruby
 sudo: false
+bundler_args: --without development
 env:
- - 'RAILS_VERSION=5.1.2'
+ matrix:
+ - "RAILS_VERSION=5.2"
+ - "RAILS_VERSION=6.0"
 rvm:
- - 2.3.3
-matrix:
-before_install: gem install bundler -v 1.13.6
+ - 2.4
+ - 2.5
+ - 2.6
+ - 2.7
 script: bundle exec rspec spec
-