Bump @babel/preset-env from 7.15.4 to 7.15.6 in /assets (#264)

Author: dependabot[bot]

assets/package-lock.json

@@ -19,7 +19,7 @@
   },
   "devDependencies": {
     "@babel/core": "^7.15.5",
-    "@babel/preset-env": "^7.15.4",
+    "@babel/preset-env": "^7.15.6",
     "babel-eslint": "^10.1.0",
     "babel-loader": "^8.2.1",
     "copy-webpack-plugin": "^9.0.1",