Attempt to fix jruby issues.

.travis.yml

@@ -1,16 +1,35 @@
----
 language: ruby
+
+sudo: false
+
+before_install:
+  - gem update --system
+  # bundler installation needed for jruby-head
+  # https://github.com/travis-ci/travis-ci/issues/5861
+  - gem install bundler
+
 script: "bundle exec rubytest -Ilib test/ --verbose"
 bundler_args: --without guard
+
 rvm:
   - 2.0.0
   - 2.1.0
   - 2.2.4
   - 2.3.2
   - 2.4.0
   - rbx
+  - jruby-9.0.5.0
+  - jruby-9.1.5.0
   - jruby-head
+
 matrix:
   allow_failures:
     - rvm: rbx
+
 cache: bundler
+
+# Use Java 8 for jruby to fix some Java 7 bugs.
+addons:
+  apt:
+    packages:
+      - oracle-java8-set-default