.travis.yml in benchmark_driver-0.14.18 vs .travis.yml in benchmark_driver-0.14.19

@@ -1,10 +1,14 @@
 language: ruby
 rvm:
-  - 2.2.8
-  - 2.3.6
-  - 2.4.3
-  - 2.5.0
+  - 2.3.8
+  - 2.4.6
+  - 2.5.5
+  - 2.6.3
+  - ruby-head
+matrix:
+  allow_failures:
+    - rvm: ruby-head
 cache: bundler
 branches:
   only:
     - master
 before_install: