Add debug tracing for JRuby code coverage

Author: bf4

.travis.yml

@@ -10,9 +10,8 @@ rvm:
   - 2.0.0
   - 2.1
   - 2.2
-  - jruby-19mode
-  - rbx-2
   - ruby-head
+  - rbx-2
 
 install:
   - bundle install --retry=3
@@ -28,6 +27,9 @@ env:
   - "RAILS_VERSION=master"
 
 matrix:
+  include:
+  - rvm: jruby-19mode
+    env: JRUBY_OPTS='--server -Xcompile.invokedynamic=false -Xcli.debug=true --debug'
   allow_failures:
     - rvm: ruby-head
     - env: "RAILS_VERSION=master"