Bump react from 16.10.2 to 16.12.0 (#12573)

Bumps [react](https://github.com/facebook/react/tree/HEAD/packages/react) from 16.10.2 to 16.12.0.
- [Release notes](https://github.com/facebook/react/releases)
- [Changelog](https://github.com/facebook/react/blob/master/CHANGELOG.md)
- [Commits](https://github.com/facebook/react/commits/v16.12.0/packages/react)

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

package.json

@@ -123,7 +123,7 @@
     "prop-types": "^15.5.10",
     "punycode": "^2.1.0",
     "rails-ujs": "^5.2.4",
-    "react": "^16.10.2",
+    "react": "^16.12.0",
     "react-dom": "^16.12.0",
     "react-hotkeys": "^1.1.4",
     "react-immutable-proptypes": "^2.1.0",