Bump webpacker from 4.2.0 to 4.2.2 (#12632)

Bumps [webpacker](https://github.com/rails/webpacker) from 4.2.0 to 4.2.2.
- [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/v4.2.0...v4.2.2)

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

Gemfile.lock

@@ -660,7 +660,7 @@ GEM
       addressable (>= 2.3.6)
       crack (>= 0.3.2)
       hashdiff (>= 0.4.0, < 2.0.0)
-    webpacker (4.2.0)
+    webpacker (4.2.2)
       activesupport (>= 4.2)
       rack-proxy (>= 0.6.1)
       railties (>= 4.2)