if oauth/personal access token is invalid, this should not blow up the program

During an `update-db` run, I stumbled upon the following crash:

```
2% complete
Retrieving GitHub token rate limits...
...complete.
Error retrieving rate limit { [Error: {"message":"Bad credentials","documentation_url":"
https://developer.github.com/v3"}]
message:
'{"message":"Bad credentials","documentation_url":"https://developer.github.com/v3"}'
,
code: 401,
```

.. which stopped the program from running. Should make it more resilient.

The crash occurs during `update-db` while retrieving GitHub token rate limits. Start by locating that rate-limit retrieval and its error handling, then check how the run responds to a 401 Bad credentials response. Done when an invalid token no longer stops the program; the issue does not name a file or test.

Written by the indexing model from the issue text.