Show file paths in stack traces

I was getting stack traces looked like this:

```
(eval):28:in `block (2 levels) in <class:Invoice>': ArgumentError (ArgumentError)
        from (eval):19:in `render'
        from (eval):120:in `block in new_screen'
        from (eval):118:in `tap'
....
```

Now it shows the file path instead of "(eval)"