Log filename that JSX parsing error occurred in

Fixes #79

## Problem
If there is an error parsing JSX, it only tells you a line number and not the file that the parsing error was in. This makes it difficult to figure out where the error is in your codebase.

## Solution
The fileName is available in the error object that gets piped through the stream, we just need to add a logging statement to make it visible.
Also added logic to strip off the `cwd` from the file path to make it easier to read (was full path from root of filesystem).

## Testing
- Cause a JSX parse error
- Check to be sure the output looks like this on a build:

![screenshot](http://content.screencast.com/users/max.peterson/folders/Jing/media/ca26ad8f-7cc8-4057-9af2-8d7506244bc7/00001185.png)

@evanweible-wf 
@trentgrover-wf 

FYI: @brentechols-wf 
`path.indexOf(cwd)` already assigned to `i`, don't need to call again