Bump importmap-rails from 0.7.6 to 0.8.1

Bumps [importmap-rails](https://github.com/rails/importmap-rails) from 0.7.6 to 0.8.1.
- [Release notes](https://github.com/rails/importmap-rails/releases)
- [Commits](https://github.com/rails/importmap-rails/compare/v0.7.6...v0.8.1)

---
updated-dependencies:
- dependency-name: importmap-rails
  dependency-type: direct:production
  update-type: version-update:semver-minor
...

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

Gemfile.lock

@@ -79,7 +79,7 @@ GEM
       activesupport (>= 5.0)
     i18n (1.8.10)
       concurrent-ruby (~> 1.0)
-    importmap-rails (0.7.6)
+    importmap-rails (0.8.1)
       rails (>= 6.0.0)
     io-console (0.5.9)
     irb (1.3.7)
@@ -93,7 +93,7 @@ GEM
       mini_mime (>= 0.1.1)
     marcel (1.0.2)
     method_source (1.0.0)
-    mini_mime (1.1.1)
+    mini_mime (1.1.2)
     mini_portile2 (2.6.1)
     minitest (5.14.4)
     msgpack (1.4.2)