.travis.yml in r10k-3.1.0 vs .travis.yml in r10k-3.1.1

@@ -1,15 +1,26 @@
 ---
 language: ruby
+services:
+  - docker
 bundler_args: "--without system"
 script: "bundle exec rspec --color --format documentation spec/unit"
 notifications:
   email: false
 sudo: false
-before_install: gem update bundler
-rvm:
-  - "2.5"
-  - "2.4"
-  - "2.3"
-  - "jruby"
 jdk:
     - oraclejdk8
+before_install: gem install bundler -v '< 2' --no-document
+matrix:
+  include:
+    - stage: r10k tests
+      rvm: 2.5.0
+    - stage: r10k tests
+      rvm: 2.4.0
+    - stage: r10k tests
+      rvm: 2.3.0
+    - stage: r10k tests
+      rvm: jruby
+    - stage: r10k container tests
+      language: generic
+      script:
+        - cd docker && make lint && make build && make test