.travis.yml in rubocop-thread_safety-0.3.4 vs .travis.yml in rubocop-thread_safety-0.4.0

@@ -1,13 +1,14 @@
 sudo: false
 cache: bundler
 language: ruby
 rvm:
   - jruby-9.1.14.0
-  - 2.1
-  - 2.2
   - 2.3.0
   - 2.4
+  - 2.5
+  - 2.6
+  - 2.7
 
 matrix:
   fast_finish: true
 
 before_install: gem install --remote bundler