Add travis test and codecheck stages

Author: grzegorz-jakubiak

.travis.yml

@@ -1,14 +1,18 @@
 language: ruby
+rvm:
+  - 2.4
+  - 2.5
+  - 2.6
+  - 2.7
 services:
   - mongodb
 before_install:
   - gem update --system
   - gem install bundler
   - bundle update --bundler
-after_script:
-  - bundle exec rubocop
-rvm:
-  - 2.4
-  - 2.5
-  - 2.6
-  - 2.7
+jobs:
+  include:
+    - stage: test
+      script: bundle exec rake
+    - stage: codecheck
+      script: bundle exec rubocop