.travis.yml in x25519-1.0.3 vs .travis.yml in x25519-1.0.4

@@ -1,12 +1,21 @@
 language: ruby
+cache: bundler
 
+before_install:
+  - gem update --system
+  - gem --version
+  - gem install bundler -v 1.16.1
+  - bundle --version
+
 rvm:
-  - 2.2.8
-  - 2.3.5
-  - 2.4.2
+  - 2.2
+  - 2.3
+  - 2.4.3
+  - 2.5.0
 
-before_install: gem install bundler -v 1.16.0
+matrix:
+  fast_finish: true
 
 branches:
   only:
     - master