Fix Error_InvalidModuleDeclaration.module.js on Windows

This error reported looks like:

File not found 'c:\src\traceur\test\feature\Modules\resources\no_such_file.js'

We were not correctly normalizing this error.

Fixes #1322
I think its more like "Only one of our tests happen to use absolute paths". That is, I don't think we have logic to report errors using relative UNIX paths, it just happens that our tests only have such errors.