as.tree fails

Reproducible example:

```
library(reprtree)
library(randomForest)
data(spam, package="kernlab")

rf <- randomForest(type ~. , data = spam, ntree = 10)
as.tree(getTree(rf, 1, labelVar = T), rf)
```

Produces:

```
Error in match.fun(FUN) : object 'factor.repr' not found
```
