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
The other way to solve this is to blindly change all backslashes to forward and write the expected values with forward slashes. That avoids the mysterious regular expression.