.travis.yml in strong_json-2.1.1 vs .travis.yml in strong_json-2.1.2

@@ -1,4 +1,5 @@
 language: ruby
 rvm:
-  - "2.5.3"
-  - "2.6.3"
+  - "2.5.8"
+  - "2.6.6"
+  - "2.7.1"