Merge pull request #161 from activeadmin/dependabot/bundler/rack-2.2.3

Author: dependabot[bot]

Gemfile.lock

@@ -178,7 +178,7 @@ GEM
     pry-rails (0.3.8)
       pry (>= 0.10.4)
     public_suffix (3.0.3)
-    rack (2.0.8)
+    rack (2.2.3)
     rack-test (1.1.0)
       rack (>= 1.0, < 3)
     rails (5.2.3)