Fix issue with find_assets on staging

[Chocksy]

Sprockets 3 changed the way it works so now our find_assets line in application.html doesn't work in production because it returns nil. We could turn compile on on staging/prod but that's not ideal as it will compile assets each time or we can find another way to access the assets and check if the js file exists.

2016-03-03T09:12:20.814810+00:00 app[web.1]: App 138 stdout: ActionView::Template::Error (undefined method `find_asset' for nil:NilClass):
2016-03-03T09:12:20.814829+00:00 app[web.1]: App 138 stdout:     14:   %body{:id=>"#{controller.controller_name}-#{controller.action_name}"}
2016-03-03T09:12:20.814848+00:00 app[web.1]: App 138 stdout:     15:     = yield
2016-03-03T09:12:20.814887+00:00 app[web.1]: App 138 stdout:     16:     = javascript_include_tag 'application', 'data-turbolinks-eval' => false
2016-03-03T09:12:20.814906+00:00 app[web.1]: App 138 stdout:     17:     - if Rails.application.assets.find_asset("pages/#{controller.controller_name}")
2016-03-03T09:12:20.814932+00:00 app[web.1]: App 138 stdout:     18:       = javascript_include_tag "pages/#{controller.controller_name}"
2016-03-03T09:12:20.814967+00:00 app[web.1]: App 138 stdout: 
2016-03-03T09:12:20.814750+00:00 app[web.1]: App 138 stdout: 
2016-03-03T09:12:20.814848+00:00 app[web.1]: App 138 stdout:     15:     = yield
2016-03-03T09:12:20.880840+00:00 app[web.1]: App 159 stdout: 

rails/sprockets-rails#294
mileszs/wicked_pdf#476