Use sprockets version 3.7.2

Various suggestions to downgrade sprockets to fix a segfault crash:

sass/sassc-ruby#207
sass/sassc-rails#122
rails/sprockets#633

We'll see if that fixes it for us.

Refs: #2872

Gemfile

@@ -35,6 +35,7 @@ gem "webpacker", "~> 5.x"
 gem "cocoon", "~> 1.2"
 
 gem "sass-rails", "~> 6.0"
+gem "sprockets", "3.7.2"
 gem "normalize-rails", "~> 4.1"
 
 gem "rails-i18n", "~> 6.0.0"

Gemfile.lock

@@ -467,7 +467,7 @@ GEM
     spring-watcher-listen (2.0.1)
       listen (>= 2.7, < 4.0)
       spring (>= 1.2, < 3.0)
-    sprockets (4.0.2)
+    sprockets (3.7.2)
       concurrent-ruby (~> 1.0)
       rack (> 1, < 3)
     sprockets-rails (3.2.2)
@@ -605,6 +605,7 @@ DEPENDENCIES
   simple_form (~> 5.0)
   spring (~> 2.0)
   spring-watcher-listen (~> 2.0)
+  sprockets (= 3.7.2)
   standard
   textacular (~> 5.1)
   timecop (~> 0.9)

config/initializers/assets.rb

@@ -10,4 +10,29 @@
 # Rails.application.config.assets.paths << Emoji.images_path
 
 # Precompile additional assets.
-Rails.application.config.assets.precompile = ["manifest.js"]
+# application.js, application.css, and all non-JS/CSS in app/assets folder are already added.
+Rails.application.config.assets.precompile += %w(
+  email.css
+
+  public.css
+  admin.css
+  chapter_ambassador.css
+  student.css
+  mentor.css
+  judge.css
+
+  printable_scores.css
+
+  public.js
+  admin.js
+  chapter_ambassador.js
+  student.js
+  mentor.js
+  judge.js
+
+  location-details.js
+
+  location-based-search.js
+  text-based-search.js
+  toggle-based-search.js
+)