Bump sprockets from 2.12.4 to 2.12.5

Bumps [sprockets](https://github.com/rails/sprockets) from 2.12.4 to 2.12.5.
- [Release notes](https://github.com/rails/sprockets/releases)
- [Changelog](https://github.com/rails/sprockets/blob/master/CHANGELOG.md)
- [Commits](rails/sprockets@v2.12.4...v2.12.5)

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

Author: dependabot[bot]

Gemfile.lock

@@ -57,7 +57,7 @@ GEM
       mime-types (>= 1.16, < 3)
     mime-types (2.6.2)
     minitest (4.7.5)
-    multi_json (1.11.2)
+    multi_json (1.15.0)
     pg (0.17.1)
     rack (1.5.5)
     rack-test (0.6.3)
@@ -102,7 +102,7 @@ GEM
       sass (~> 3.2.2)
       sprockets (~> 2.8, < 3.0)
       sprockets-rails (~> 2.0)
-    sprockets (2.12.4)
+    sprockets (2.12.5)
       hike (~> 1.2)
       multi_json (~> 1.0)
       rack (~> 1.0)