Bump @babel/polyfill from 7.4.4 to 7.6.0 in /js

Bumps [@babel/polyfill](https://github.com/babel/babel) from 7.4.4 to 7.6.0.
- [Release notes](https://github.com/babel/babel/releases)
- [Changelog](https://github.com/babel/babel/blob/master/CHANGELOG.md)
- [Commits](https://github.com/babel/babel/compare/v7.4.4...v7.6.0)

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

js/package.json

@@ -28,7 +28,7 @@
   "devDependencies": {
     "@babel/core": "^7.5.5",
     "@babel/plugin-syntax-dynamic-import": "^7.2.0",
-    "@babel/polyfill": "^7.4.4",
+    "@babel/polyfill": "^7.6.0",
     "@babel/preset-env": "^7.5.5",
     "babel-loader": "^8.0.6",
     "css-loader": "^3.2.0",