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>

Author: dependabot[bot]

Gemfile.lock

@@ -64,7 +64,7 @@ GEM
       coffee-script-source
       execjs
     coffee-script-source (1.12.2)
-    concurrent-ruby (1.0.5)
+    concurrent-ruby (1.1.10)
     crass (1.0.3)
     erubi (1.7.0)
     execjs (2.7.0)
@@ -97,7 +97,7 @@ GEM
     public_suffix (3.0.1)
     puma (3.11.0)
     racc (1.6.0)
-    rack (2.0.3)
+    rack (2.2.3)
     rack-test (0.8.2)
       rack (>= 1.0, < 3)
     rails (5.1.4)
@@ -142,7 +142,7 @@ GEM
     selenium-webdriver (3.8.0)
       childprocess (~> 0.5)
       rubyzip (~> 1.0)
-    sprockets (3.7.1)
+    sprockets (3.7.2)
       concurrent-ruby (~> 1.0)
       rack (> 1, < 3)
     sprockets-rails (3.2.1)