Bump webpack-merge from 4.1.5 to 4.2.1 in /js

Bumps [webpack-merge](https://github.com/survivejs/webpack-merge) from 4.1.5 to 4.2.1.
- [Release notes](https://github.com/survivejs/webpack-merge/releases)
- [Changelog](https://github.com/survivejs/webpack-merge/blob/master/CHANGELOG.md)
- [Commits](https://github.com/survivejs/webpack-merge/compare/v4.1.5...v4.2.1)

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

js/package-lock.json

@@ -7108,9 +7108,9 @@
       }
     },
     "webpack-merge": {
-      "version": "4.1.5",
-      "resolved": "https://registry.npmjs.org/webpack-merge/-/webpack-merge-4.1.5.tgz",
-      "integrity": "sha512-sVcM+MMJv6DO0C0GLLltx8mUlGMKXE0zBsuMqZ9jz2X9gsekALw6Rs0cAfTWc97VuWS6NpVUa78959zANnMMLQ==",
+      "version": "4.2.1",
+      "resolved": "https://registry.npmjs.org/webpack-merge/-/webpack-merge-4.2.1.tgz",
+      "integrity": "sha512-4p8WQyS98bUJcCvFMbdGZyZmsKuWjWVnVHnAS3FFg0HDaRVrPbkivx2RYCre8UiemD67RsiFFLfn4JhLAin8Vw==",
       "dev": true,
       "requires": {
         "lodash": "^4.17.5"

js/package.json

@@ -32,7 +32,7 @@
     "uglifyjs-webpack-plugin": "^2.1.1",
     "webpack": "^4.28.3",
     "webpack-cli": "^3.1.2",
-    "webpack-merge": "^4.1.5"
+    "webpack-merge": "^4.2.1"
   },
   "scripts": {
     "build": "./node_modules/webpack-cli/bin/cli.js --mode production --config webpack.prod.config.js",