Report syntax errors in JavaScript code to help troubleshooting

Similar to #5, but for syntax errors in JavaScript.

```
require-lint --pkg test/bad-syntax/package.json --src index.js
/dev/require-lint/test/bad-syntax/index.js
Line 4: Unexpected token )
```

```
require-lint --pkg test/bad-syntax/package.json --require "coffee-script/register" --src index.coffee
/dev/require-lint/test/bad-syntax/index.coffee
Line 3: unmatched )
```