.travis.yml in ledger_sync-1.3.5 vs .travis.yml in ledger_sync-1.4.0

@@ -1,9 +1,13 @@
 ---
 language: ruby
 cache: bundler
 rvm:
+  - 2.5.8
   - 2.6.6
+  - 2.6.3
+  - 2.7.1
+  # - ruby-head
 before_install:
   - gem update --system
   - gem install bundler:1.17.3
 script:
   - bundle exec rspec --order rand