Bump @rails/webpacker from 4.0.7 to 4.2.0

Bumps [@rails/webpacker](https://github.com/rails/webpacker) from 4.0.7 to 4.2.0.
- [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/v4.0.7...v4.2.0)

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

package.json

@@ -1,6 +1,6 @@
 {
   "dependencies": {
-    "@rails/webpacker": "4.0",
+    "@rails/webpacker": "4.2",
     "bootstrap": "^4.1.3",
     "bootswatch": "^4.4.1",
     "chosen-js": "^1.8.7",