Bump sprockets

Gemfile

@@ -114,7 +114,7 @@ group :production do
   gem 'dalli', '~> 2.7.6'
 end
 
-gem 'sprockets',        '~> 2.12.3'
+gem 'sprockets',        '~> 3.5.2'
 gem 'sass-rails',       '~> 5.0.3'
 gem 'sass',             '~> 3.4.12'
 gem 'autoprefixer-rails'

Gemfile.lock

@@ -189,6 +189,7 @@ GEM
     coercible (1.0.0)
       descendants_tracker (~> 0.0.1)
     color-tools (1.3.0)
+    concurrent-ruby (1.0.1)
     crack (0.4.2)
       safe_yaml (~> 1.0.0)
     crowdin-api (0.4.0)
@@ -293,7 +294,6 @@ GEM
     hashie (3.4.1)
     health_check (1.5.1)
       rails (>= 2.3.0)
-    hike (1.2.3)
     htmldiff (0.0.1)
     http-cookie (1.0.2)
       domain_name (~> 0.5)
@@ -515,11 +515,9 @@ GEM
       simplecov-html (~> 0.7.1)
     simplecov-html (0.7.1)
     slop (3.6.0)
-    sprockets (2.12.4)
-      hike (~> 1.2)
-      multi_json (~> 1.0)
-      rack (~> 1.0)
-      tilt (~> 1.1, != 1.3.0)
+    sprockets (3.5.2)
+      concurrent-ruby (~> 1.0)
+      rack (> 1, < 3)
     sprockets-rails (2.3.3)
       actionpack (>= 3.0)
       activesupport (>= 3.0)
@@ -535,7 +533,7 @@ GEM
       rack (~> 1.0)
     thor (0.19.1)
     thread_safe (0.3.5)
-    tilt (1.4.1)
+    tilt (2.0.2)
     timecop (0.7.3)
     ttfunk (1.4.0)
     tzinfo (1.2.2)
@@ -674,7 +672,7 @@ DEPENDENCIES
   shoulda-context (~> 1.2)
   shoulda-matchers (~> 2.8)
   simplecov (= 0.8.0.pre)
-  sprockets (~> 2.12.3)
+  sprockets (~> 3.5.2)
   sqlite3
   svg-graph!
   syck (~> 1.0.5)