Fixing java unit test

For some reason, the class path in the backtrace has changed.

Author: sponte

features/docs/cli/backtraces.feature

@@ -31,6 +31,6 @@ Feature: Backtraces
         Scenario: Example # features/failing_hard.feature:2
           Given failing   # features/step_definitions/steps.rb:4
              (Java::JavaLang::UnsupportedOperationException)
-            java.util.AbstractList.add(AbstractList.java:
+            java.util.AbstractList.add(java/util/AbstractList.java:
       """