.travis.yml in heartcheck-1.5.1 vs .travis.yml in heartcheck-1.6.0

@@ -17,5 +17,7 @@
       gemfile: Gemfile-old-ruby
     - rvm: "2.2.2"
     - rvm: "2.3.0"
     - rvm: "2.3.3"
     - rvm: "2.4.1"
+    - rvm: "2.5.7"
+    - rvm: "2.6.5"