Heroku is failing - raising OSError when making LOGS_DIR

[CasperWA]

From the heroku logs:

2020-08-02T18:12:41.473090+00:00 app[web.1]: File "./optimade/server/logger.py", line 39, in <module>
2020-08-02T18:12:41.473090+00:00 app[web.1]: LOGS_DIR.mkdir(exist_ok=True)
2020-08-02T18:12:41.473093+00:00 app[web.1]: File "/app/.heroku/python/lib/python3.7/pathlib.py", line 1268, in mkdir
2020-08-02T18:12:41.473093+00:00 app[web.1]: self._accessor.mkdir(self, mode)
2020-08-02T18:12:41.473136+00:00 app[web.1]: OSError: [Errno 30] Read-only file system: '/var/log/optimade'
2020-08-02T18:13:38.829133+00:00 heroku[web.1]: Error R10 (Boot timeout) -> Web process failed to bind to $PORT within 60 seconds of launch

So it seems we should "simply" try and catch a more general OSError instead of PermissionError when trying to make the directory.