.travis.yml in rumale-0.14.5 vs .travis.yml in rumale-0.15.0

@@ -4,9 +4,10 @@
 language: ruby
 rvm:
   - '2.4'
   - '2.5'
   - '2.6'
+  - '2.7'
 
 addons:
   apt:
     packages:
       - libopenblas-dev