[#174917481] failure loading image from URL in sass

As per this thread ( rails/sprockets#581 ),  Try disabling concurrent asset processing.

Also updated sass for good measure.

[#174917481]

Author: knowuh

rails/Gemfile

@@ -85,7 +85,7 @@ gem 'rollbar'
 gem 'rubyzip',              '~> 1.2.2'
 gem 'rush',                 git: 'https://github.com/concord-consortium/rush.git'
 gem 'sanitize'
-gem 'sass',                 '~> 3.4.0'
+gem 'sass',                 '~> 3.7.4'
 gem 'sass-rails' # if running rails 3.1 or greater
 # gem 'strong_parameters'  # RAILS-4-SPIKE GEMFILE REMOVE as part of rails 4.0 upgrade
 gem 'sunspot_rails'

rails/Gemfile.lock

@@ -765,7 +765,7 @@ GEM
       execjs
     coffee-script-source (1.12.2)
     columnize (0.9.0)
-    concurrent-ruby (1.1.7)
+    concurrent-ruby (1.1.8)
     connection_pool (2.2.2)
     crack (0.4.3)
       safe_yaml (~> 1.0.0)
@@ -838,8 +838,8 @@ GEM
       activesupport (>= 3.0.0)
     faraday (0.12.1)
       multipart-post (>= 1.2, < 3)
-    ffi (1.13.1)
-    ffi (1.13.1-x86-mingw32)
+    ffi (1.14.2)
+    ffi (1.14.2-x86-mingw32)
     font-awesome-rails (4.7.0.1)
       railties (>= 3.2, < 5.1)
     formatador (0.2.5)
@@ -1102,7 +1102,11 @@ GEM
       crass (~> 1.0.2)
       nokogiri (>= 1.4.4)
       nokogumbo (= 1.4.1)
-    sass (3.4.25)
+    sass (3.7.4)
+      sass-listen (~> 4.0.0)
+    sass-listen (4.0.0)
+      rb-fsevent (~> 0.9, >= 0.9.4)
+      rb-inotify (~> 0.9, >= 0.9.7)
     sass-rails (6.0.0)
       sassc-rails (~> 2.1, >= 2.1.1)
     sassc (2.4.0)
@@ -1313,7 +1317,7 @@ DEPENDENCIES
   rubyzip (~> 1.2.2)
   rush!
   sanitize
-  sass (~> 3.4.0)
+  sass (~> 3.7.4)
   sass-rails
   selenium-webdriver
   sextant

rails/config/application.rb

@@ -148,6 +148,7 @@ class Application < Rails::Application
     config.middleware.insert_before 0, "Rack::ResponseLogger"
 
     config.assets.enabled = true
+    config.assets.export_concurrent = false
     config.assets.precompile += %w(
       print.css
       full_status.js