DB container does not initialise correctly

https://github.com/Dagefoerde/Moodledocker/blob/a0a99e8b1a50ded86c6220b65f7261bfbdd08296/Dockerfiles/moodlepostgres/moodlebase.sh fails. As a result, Moodle user and pass are not created inside fresh DB containers.

Output:
```
db_1     | error: failed switching to "postgres": operation not permitted
m33_db_1 exited with code 1
```