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

@@ -60,7 +60,7 @@ GEM
       coffee-script-source
       execjs
     coffee-script-source (1.12.2)
-    concurrent-ruby (1.0.5)
+    concurrent-ruby (1.1.8)
     crass (1.0.2)
     erubi (1.7.0)
     execjs (2.7.0)
@@ -102,7 +102,7 @@ GEM
     public_suffix (3.0.0)
     puma (3.10.0)
     racc (1.5.2)
-    rack (2.0.3)
+    rack (2.2.3)
     rack-test (0.7.0)
       rack (>= 1.0, < 3)
     rails (5.1.4)
@@ -153,7 +153,7 @@ GEM
     spring-watcher-listen (2.0.1)
       listen (>= 2.7, < 4.0)
       spring (>= 1.2, < 3.0)
-    sprockets (3.7.1)
+    sprockets (3.7.2)
       concurrent-ruby (~> 1.0)
       rack (> 1, < 3)
     sprockets-rails (3.2.1)