update travis matrix (add truffleruby, remove rubinius) (#695)

.travis.yml

@@ -19,10 +19,10 @@ matrix:
       script: bundle exec rake test_cov
     - name: jruby-9.1.15.0 / Parser tests
       rvm: jruby-9.1.15.0
-      script: bundle exec rake test_cov
-    - name: rbx-2 / Parser tests
-      rvm: rbx-2
-      script: bundle exec rake test_cov
+      script: bundle exec rake test
+    - name: truffleruby / Parser tests
+      rvm: truffleruby
+      script: bundle exec rake test
     - name: 2.5.8 / Rubocop tests
       rvm: 2.5.8
       script: ./ci/run_rubocop_specs
@@ -34,7 +34,6 @@ matrix:
       script: ./ci/run_rubocop_specs
   allow_failures:
     - rvm: ruby-head
-    - rvm: rbx-2
     - script: ./ci/run_rubocop_specs
 before_install:
   - bundle --version