Fix webpack build issues

This upgrades @babel/preset-env to 7.9.0 from 7.8.7.

See: https://github.com/nodejs/node/issues/32852#issuecomment-613655150

prose/package.json

@@ -16,7 +16,7 @@
   },
   "devDependencies": {
     "@babel/core": "^7.8.7",
-    "@babel/preset-env": "^7.8.7",
+    "@babel/preset-env": "^7.9.0",
     "babel-loader": "^8.0.6"
   },
   "scripts": {