[Bridge][Monolog] fix monolog handler

| Q             | A
| ------------- | ---
| Bug fix?      | yes
| New feature?  | no
| BC breaks?    | no
| Deprecations? | no
| Tests pass?   | yes
| License       | MIT

see also https://github.com/Seldaek/monolog/commit/e0d18f454be4b149e528ade4a6852cf2493f4302