Bump sprockets from 3.7.1 to 3.7.2

Bumps [sprockets](https://github.com/rails/sprockets) from 3.7.1 to 3.7.2.
- [Release notes](https://github.com/rails/sprockets/releases)
- [Changelog](https://github.com/rails/sprockets/blob/v3.7.2/CHANGELOG.md)
- [Commits](rails/sprockets@v3.7.1...v3.7.2)

Signed-off-by: dependabot[bot] <support@github.com>

Gemfile.lock

@@ -215,7 +215,7 @@ GEM
       method_source (~> 0.9.0)
     public_suffix (3.0.1)
     puma (3.11.0)
-    rack (2.0.3)
+    rack (2.0.7)
     rack-test (0.8.2)
       rack (>= 1.0, < 3)
     rails (5.1.4)
@@ -282,7 +282,7 @@ GEM
       json (>= 1.8, < 3)
       simplecov-html (~> 0.10.0)
     simplecov-html (0.10.2)
-    sprockets (3.7.1)
+    sprockets (3.7.2)
       concurrent-ruby (~> 1.0)
       rack (> 1, < 3)
     sprockets-rails (3.2.1)