Fix for unwanted modification of original data while dumping

There is a bug in the Dancer::Error::dumper function.
If you don't have Clone module installed on your system (which is neither a standard module nor a prerequisite for Dancer) then Dancer can modify the original data while "censoring" it. 

For example, if you are running under a persistent environment and your app config has something like
```yaml
facebook:
    app_id: 123
    app_secret: abc
```
then once it is dumped (which happens automatically if you have "show_errors" enabled) the config becomes corrupted and all subsequent requests that use that config will fail.