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

Gemfile.lock

@@ -609,9 +609,9 @@ GEM
     sprockets (4.2.1)
       concurrent-ruby (~> 1.0)
       rack (>= 2.2.4, < 4)
-    sprockets-rails (3.2.2)
-      actionpack (>= 4.0)
-      activesupport (>= 4.0)
+    sprockets-rails (3.4.2)
+      actionpack (>= 5.2)
+      activesupport (>= 5.2)
       sprockets (>= 3.0.0)
     sshkit (1.22.0)
       mutex_m

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]