Make buffy less sensitive to space

I'd expect both commands to work

```
@ropensci-review-bot set due date for @bla to 2024-03-25
```


```
@ropensci-review-bot set due date for @bla  to 2024-03-25
```

but the second does not, due to the two space characters after "bla".

Obviously parking this for later, there's no active development of ropensci-org/buffy at the moment.