Bump rails-dom-testing from 2.0.3 to 2.1.1

Bumps [rails-dom-testing](https://github.com/rails/rails-dom-testing) from 2.0.3 to 2.1.1.
- [Release notes](https://github.com/rails/rails-dom-testing/releases)
- [Commits](rails/rails-dom-testing@v2.0.3...v2.1.1)

---
updated-dependencies:
- dependency-name: rails-dom-testing
  dependency-type: indirect
  update-type: version-update:semver-minor
...

Signed-off-by: dependabot[bot] <[email protected]>

Gemfile.lock

@@ -220,8 +220,9 @@ GEM
       actionpack (>= 5.0.1.rc1)
       actionview (>= 5.0.1.rc1)
       activesupport (>= 5.0.1.rc1)
-    rails-dom-testing (2.0.3)
-      activesupport (>= 4.2.0)
+    rails-dom-testing (2.1.1)
+      activesupport (>= 5.0.0)
+      minitest
       nokogiri (>= 1.6)
     rails-html-sanitizer (1.6.0)
       loofah (~> 2.21)