Test JRuby 9.2 on Travis

Also, add workaround for bundler install on older ruby.

Author: jeremyevans

.travis.yml

@@ -13,6 +13,7 @@ rvm:
   - jruby-19mode
   - jruby-9.0.5.0
   - jruby-9.1.12.0
+  - jruby-9.2.8.0
   - jruby-head
   - ruby-head
   - truffleruby
@@ -22,3 +23,5 @@ matrix:
     - rvm: ruby-head
     - rvm: truffleruby
 gemfile: .travis.gemfile
+before_install:
+  - gem install bundler || gem install bundler --version '< 2'