pass transform errors out as top-level exceptions

If an error occurs when converting the jsx into js, send a valid
200 response to the browser containing a top-level javascript
error that indicates the problem, rather than sending a 500 in
which the cause of the error ends up being swallowed.
update test to new error handling
Merge pull request #1 from jut-io/convert-transform-errors

pass transform errors out as top-level exceptions