.travis.yml in benchmark_driver-0.15.7 vs .travis.yml in benchmark_driver-0.15.8

@@ -1,10 +1,11 @@
 language: ruby
 rvm:
   - 2.3.8
-  - 2.4.6
-  - 2.5.5
-  - 2.6.3
+  - 2.4.9
+  - 2.5.7
+  - 2.6.5
+  - 2.7.0
   - ruby-head
 matrix:
   allow_failures:
     - rvm: ruby-head
 cache: bundler