.travis.yml in grpc_mock-0.2.2 vs .travis.yml in grpc_mock-0.3.0

@@ -1,6 +1,7 @@
 sudo: false
 language: ruby
 rvm:
+  - 2.6.3
   - 2.5.3
   - 2.4.5
 before_install: gem install bundler -v 1.16.1