.travis.yml in mistral_client-1.2.1 vs .travis.yml in mistral_client-1.3.0

@@ -1,10 +1,12 @@
 language: ruby
 cache: bundler
 rvm:
-  - 2.3.5
-  - 2.4.2
+  - 2.3.8
+  - 2.4.10
+  - 2.5.8
+  - 2.6.6
 before_install:
-  - rvm @global do gem install bundler
+  - gem install bundler
 branches:
   only:
     - master