Only include original line info in stack trace when using source map

I don't think it's useful at all to list the compiled line number/column in stack traces, especially since it's displayed first before the original line number/column info from the source map.  Especially when using something like browserify, you get these horribly useless paths to look at.  For example:

```
at /var/folders/_p/kll4xqzn0hn9znq6607nr14m0000gn/T/a5fdf7b6ec86e5a5a2a6f44ed6234a6791e3a679.browserify:203:0 <- /Users/devongovett/projects/editor/node_modules/chai/lib/chai/assertion.js:110:0
```

This commit removes the compiled line information from stack traces and only displays the original line information.  The output of the above example would just be:

```
at /Users/devongovett/projects/Storify/editor/node_modules/chai/lib/chai/assertion.js:110:0
```