Bump sprockets from 3.7.2 to 4.0.2

Bumps [sprockets](https://github.com/rails/sprockets) from 3.7.2 to 4.0.2.
- [Release notes](https://github.com/rails/sprockets/releases)
- [Changelog](https://github.com/rails/sprockets/blob/master/CHANGELOG.md)
- [Commits](rails/sprockets@v3.7.2...v4.0.2)

---
updated-dependencies:
- dependency-name: sprockets
  dependency-type: direct:production
  update-type: version-update:semver-major
...

(Comment by Javi Martín): After this upgrade, compiling the assets is
significantly slower. Also note we need to explicitely include CKEditor
assets and the default application assets and images; we didn't have to
do so in the past.

Signed-off-by: dependabot[bot] <[email protected]>

Gemfile

@@ -51,7 +51,7 @@ gem "sassc-rails", "~> 2.1.2"
 gem "savon", "~> 2.12.1"
 gem "sitemap_generator", "~> 6.1.2"
 gem "social-share-button", "~> 1.2.4"
-gem "sprockets", "~> 3.7.2"
+gem "sprockets", "~> 4.0.2"
 gem "translator-text", "~> 0.1.0"
 gem "turbolinks", "~> 5.2.1"
 gem "turnout", "~> 2.5.0"

Gemfile.lock

@@ -611,7 +611,7 @@ GEM
  spring (2.1.1)
  spring-commands-rspec (1.0.4)
  spring (>= 0.9.1)
- sprockets (3.7.2)
+ sprockets (4.0.2)
  concurrent-ruby (~> 1.0)
  rack (> 1, < 3)
  sprockets-es6 (0.9.2)
@@ -778,7 +778,7 @@ DEPENDENCIES
  social-share-button (~> 1.2.4)
  spring (~> 2.1.1)
  spring-commands-rspec (~> 1.0.4)
- sprockets (~> 3.7.2)
+ sprockets (~> 4.0.2)
  translator-text (~> 0.1.0)
  turbolinks (~> 5.2.1)
  turnout (~> 2.5.0)

app/assets/config/manifest.js

@@ -0,0 +1,14 @@
+//= link ckeditor/application.css
+//= link ckeditor/application.js
+//
+//= link_tree ../images
+//= link application.css
+//= link application-rtl.css
+//= link application.js
+//
+//= link ckeditor/config.js
+//= link stat_graphs.js
+//= link dashboard_graphs.js
+//= link print.css
+//= link pdf_fonts.css
+//= link_tree ../../../vendor/assets/images