[Security] Bump sprockets from 3.7.1 to 3.7.2 in /src/api

Bumps [sprockets](http://getsprockets.org/) from 3.7.1 to 3.7.2. **This update includes security fixes.**

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

src/api/Gemfile.lock

@@ -80,7 +80,7 @@ GEM
       execjs
     coffee-script-source (1.11.1)
     colorize (0.8.1)
-    concurrent-ruby (1.0.4)
+    concurrent-ruby (1.0.5)
     coveralls (0.8.19)
       json (>= 1.8, < 3)
       simplecov (~> 0.12.0)
@@ -200,7 +200,7 @@ GEM
     public_suffix (2.0.5)
     pundit (1.1.0)
       activesupport (>= 3.0.0)
-    rack (2.0.1)
+    rack (2.0.5)
     rack-test (0.6.3)
       rack (>= 1.0)
     rails (5.0.1)
@@ -296,7 +296,7 @@ GEM
       rake
     slop (3.6.0)
     sprite-factory (1.7.1)
-    sprockets (3.7.1)
+    sprockets (3.7.2)
       concurrent-ruby (~> 1.0)
       rack (> 1, < 3)
     sprockets-rails (3.1.1)