update sprockets-rails, require 3.4.2

A bug in sprockets-rails made us lock to old sprockets at #1501

Bug is fixed in sprockets-rails 3.4.2, upgrade to that now.

Gemfile

@@ -63,9 +63,7 @@ gem 'jbuilder', '~> 2.5'
 gem 'bootsnap', '>= 1.4.4', require: false
 
 gem 'bootstrap', '~> 4.3'
-# bootstrap gem requirement. Lock to 3.2.2 due to https://github.com/sciencehistory/scihist_digicoll/issues/1501
-# until https://github.com/rails/sprockets-rails/issues/488 is fixed.
-gem 'sprockets-rails', '= 3.2.2'
+gem 'sprockets-rails', '>= 3.4.2'
 
 gem 'jquery-rails', "~> 4.3"
 

Gemfile.lock

@@ -361,7 +361,7 @@ GEM
       activesupport (>= 4)
       railties (>= 4)
       request_store (~> 1.0)
-    loofah (2.12.0)
+    loofah (2.13.0)
       crass (~> 1.0.2)
       nokogiri (>= 1.5.9)
     mail (2.7.1)
@@ -599,9 +599,9 @@ GEM
     sprockets (4.0.2)
       concurrent-ruby (~> 1.0)
       rack (> 1, < 3)
-    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)
     thor (1.1.0)
     thread_safe (0.3.6)
@@ -740,7 +740,7 @@ DEPENDENCIES
   sitemap_generator (~> 6.0)
   solr_wrapper (~> 3.0, >= 3.0.1)
   sprockets (~> 4.0)
-  sprockets-rails (= 3.2.2)
+  sprockets-rails (>= 3.4.2)
   traject (>= 3.5)
   uglifier (>= 1.3.0)
   uppy-s3_multipart