Bump webpacker from 5.4.0 to 5.4.2 (#16648)

Bumps [webpacker](https://github.com/rails/webpacker) from 5.4.0 to 5.4.2.
- [Release notes](https://github.com/rails/webpacker/releases)
- [Changelog](https://github.com/rails/webpacker/blob/master/CHANGELOG.md)
- [Commits](https://github.com/rails/webpacker/compare/v5.4.0...v5.4.2)

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

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

Co-authored-by: dependabot[bot] <49699333+dependabot[bot]@users.noreply.github.com>

Gemfile.lock

@@ -437,7 +437,7 @@ GEM
       rack (>= 1.0, < 3)
     rack-cors (1.1.1)
       rack (>= 2.0.0)
-    rack-proxy (0.6.5)
+    rack-proxy (0.7.0)
       rack
     rack-test (1.1.0)
       rack (>= 1.0, < 3)
@@ -646,7 +646,7 @@ GEM
       addressable (>= 2.8.0)
       crack (>= 0.3.2)
       hashdiff (>= 0.4.0, < 2.0.0)
-    webpacker (5.4.0)
+    webpacker (5.4.2)
       activesupport (>= 5.2)
       rack-proxy (>= 0.6.1)
       railties (>= 5.2)