Error message is stripped if stack exists

It seems as though the error's message is stripped if a stack trace is present ([ParsedError.coffee:25](https://github.com/AriaMinaei/pretty-error/blob/master/src/ParsedError.coffee#L25)):

```
if typeof @_stack is 'string'
@_parseStack()
else
@_message = @error.message? and String(@error.message) or ''
```

Resulting in something like:

(when no stack is present)

And this when there **is** a stack:

Start in src/ParsedError.coffee at line 25 and read how the message is assigned when a stack trace is present versus absent. Reproduce the two reported cases, then confirm that errors with stacks retain their messages while the existing no-stack behavior remains unchanged.

Written by the indexing model from the issue text.