Change to use latest Rubies and restrict bundler version

.travis.yml

@@ -1,25 +1,24 @@
 ---
 language: ruby
-sudo: false
-cache: bundler
+before_install: "gem install bundler -v '< 2.0'"
 bundler_args: --without dev
-script: "bundle exec rake ci"
+script: bundle exec rake ci
 rvm:
-  - 1.9.3
-  - 2.0
-  - 2.1
-  - 2.2
-  - 2.3.1
+  - 2.0.0
+  - 2.1.10
+  - 2.2.10
+  - 2.3.8
+  - 2.4.6
+  - 2.5.5
+  - 2.6.3
   - ruby-head
-  - jruby-9000
+  - jruby-9.2.6.0
   - jruby-head
-  - rbx-2
 matrix:
   allow_failures:
     - rvm: ruby-head
-    - rvm: jruby-9000
     - rvm: jruby-head
-    - rvm: rbx-2
+    - rvm: jruby-9.2.6.0
   fast_finish: true
 branches:
   only: master