Ensure webpack:compile is called when running Jenkins

The "unit" tests also include system tests.

lib/discovery.rake

@@ -19,7 +19,8 @@ end
 
 load 'tasks/jenkins.rake'
 if Rake::Task.task_defined?(:'jenkins:unit')
-  Rake::Task["jenkins:unit"].enhance do
+  # The "unit" tests also include system tests
+  Rake::Task["jenkins:unit"].enhance(['webpack:compile']) do
     Rake::Task['test:discovery'].invoke
   end
 end