.travis.yml in async-rspec-1.5.0 vs .travis.yml in async-rspec-1.6.0

@@ -1,17 +1,23 @@
 language: ruby
 sudo: false
 dist: trusty
 cache: bundler
-rvm:
-  - 2.2
-  - 2.3
-  - 2.4
-  - 2.5
-  - jruby-head
-  - ruby-head
-  - rbx-3
+
+before_script:
+  - gem update --system
+  - gem install bundler
+
 matrix:
+  include:
+    - rvm: 2.3
+    - rvm: 2.4
+    - rvm: 2.5
+    - rvm: 2.6
+    - rvm: jruby-head
+      env: JRUBY_OPTS="--debug -X+O"
+    - rvm: ruby-head
+    - rvm: rbx-3
   allow_failures:
     - rvm: ruby-head
     - rvm: jruby-head
     - rvm: rbx-3