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
Yes, we only have paths in module tests, hence the original code only applies to that directory.

But if the error message is `invalid token \` and we convert it to `invalid token /` then compare it to `invalid token /` the test passes.   I suppose there is a very remote possibility that we will incorrectly pass tests that involve backslash tokens, I think it very remote.