Bump rails_admin from 3.1.2 to 3.1.3

Bumps [rails_admin](https://github.com/sferik/rails_admin) from 3.1.2 to 3.1.3.
- [Changelog](https://github.com/railsadminteam/rails_admin/blob/v3.1.3/CHANGELOG.md)
- [Commits](https://github.com/sferik/rails_admin/compare/v3.1.2...v3.1.3)

---
updated-dependencies:
- dependency-name: rails_admin
  dependency-type: direct:production
  update-type: version-update:semver-patch
...

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

Gemfile.lock

@@ -202,7 +202,7 @@ GEM
       oauth (>= 0.4.5)
       rexml
     io-console (0.7.2)
-    irb (1.13.2)
+    irb (1.14.0)
       rdoc (>= 4.0.0)
       reline (>= 0.4.2)
     jbuilder (2.12.0)
@@ -373,7 +373,7 @@ GEM
     rails-timeago (2.20.0)
       actionpack (>= 5.2)
       activesupport (>= 5.2)
-    rails_admin (3.1.2)
+    rails_admin (3.1.3)
       activemodel-serializers-xml (>= 1.0)
       kaminari (>= 0.14, < 2.0)
       nested_form (~> 0.3)