Bump sprockets-rails from 3.2.2 to 3.4.2

Note that, since version 3.3.0, sprockets-rails uses a processor to get
digested paths for asset files [1]. This breaks the images used in
CKEditor buttons [2], so we're using the new configuration option [3] to
keep the old behavior.

[1] Pull request 476 in https://github.com/rails/sprockets-rails
[2] Issue 919 in https://github.com/galetahub/ckeditor
[3] Pull request 489 in https://github.com/rails/sprockets-rails

config/application.rb

@@ -39,6 +39,9 @@ module Consul
     # work with the _count database columns we use for caching purposes
     config.active_record.has_many_inversing = false
 
+    # Disable Sprockets AssetUrlProcessor for CKEditor compatibility
+    config.assets.resolve_assets_in_css_urls = false
+
     # Keep reading existing data in the legislation_annotations ranges column
     config.active_record.yaml_column_permitted_classes = [ActiveSupport::HashWithIndifferentAccess, Symbol]