Bump sprockets from 3.7.1 to 3.7.2 in /fixture_rails_root

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>

fixture_rails_root/Gemfile.lock

@@ -58,7 +58,7 @@ GEM
       coffee-script-source
       execjs
     coffee-script-source (1.12.2)
-    concurrent-ruby (1.0.5)
+    concurrent-ruby (1.1.5)
     erubi (1.6.1)
     execjs (2.7.0)
     ffi (1.9.18)
@@ -104,7 +104,7 @@ GEM
     nokogiri (1.8.0)
       mini_portile2 (~> 2.2.0)
     puma (3.8.2)
-    rack (2.0.3)
+    rack (2.0.7)
     rack-test (0.6.3)
       rack (>= 1.0)
     rails (5.1.2)
@@ -146,7 +146,7 @@ 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 (3.2.0)