.travis.yml in zeebe-client-0.5.0 vs .travis.yml in zeebe-client-0.6.0

@@ -2,9 +2,10 @@
 language: ruby
 rvm:
   - 2.5
   - 2.4
   - 2.3
+  - 2.6
 
 services:
   - docker
 
 script: