BSN Anonymizer sometimes generates incorrect BSN Numbers

[realrolfje]

Describe the bug
Some of the generated BSN numbers are not conforming to the non-standard 11 proof calculation as described on https://nl.wikipedia.org/wiki/Burgerservicenummer

To Reproduce
Steps to reproduce the behavior:
Run the anonymizer and check all number, and/or:
Create a unittest which generates random BSNs and check them against the rules on the mentioned wikipedia page.

Expected behavior
BSN numbers which are syntactically correct and indistinguishable from real numbers

[realrolfje]

Solved in develop branch, will be part of release 1.14