Bump mobx from 5.15.1 to 5.15.4

Bumps [mobx](https://github.com/mobxjs/mobx) from 5.15.1 to 5.15.4.
- [Release notes](https://github.com/mobxjs/mobx/releases)
- [Changelog](https://github.com/mobxjs/mobx/blob/master/CHANGELOG.md)
- [Commits](https://github.com/mobxjs/mobx/compare/5.15.1...5.15.4)

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

package.json

@@ -22,7 +22,7 @@
     "date-fns": "^2.11.1",
     "dotenv": "^8.2.0",
     "lodash": "^4.17.11",
-    "mobx": "^5.15.1",
+    "mobx": "^5.15.4",
     "mobx-react": "^6.1.4",
     "prop-types": "^15.6.2",
     "query-string": "^6.9.0",