.travis.yml in ddmemoize-1.0.0a3 vs .travis.yml in ddmemoize-1.0.0rc1

@@ -1,13 +1,18 @@
 language: ruby
 
 rvm:
   - "2.3"
   - "2.4"
+  - "2.5"
 
 branches:
   only:
     - "master"
+
+before_install:
+  - gem update --system
+  - gem install bundler -v 1.16.0
 
 cache: bundler
 
 sudo: false