Bump rails_admin from 3.1.0 to 3.1.1

Bumps [rails_admin](https://github.com/sferik/rails_admin) from 3.1.0 to 3.1.1.
- [Release notes](https://github.com/sferik/rails_admin/releases)
- [Changelog](https://github.com/railsadminteam/rails_admin/blob/master/CHANGELOG.md)
- [Commits](https://github.com/sferik/rails_admin/compare/v3.1.0...v3.1.1)

---
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

@@ -138,7 +138,7 @@ GEM
       activerecord (>= 5.a)
       database_cleaner-core (~> 2.0.0)
     database_cleaner-core (2.0.1)
-    date (3.3.1)
+    date (3.3.3)
     debug_inspector (1.1.0)
     diff-lcs (1.5.0)
     docile (1.4.0)
@@ -344,7 +344,7 @@ GEM
     rails-timeago (2.20.0)
       actionpack (>= 5.2)
       activesupport (>= 5.2)
-    rails_admin (3.1.0)
+    rails_admin (3.1.1)
       activemodel-serializers-xml (>= 1.0)
       kaminari (>= 0.14, < 2.0)
       nested_form (~> 0.3)