Do not use absolute paths in test fixtures

In cases like, we should not have to update the paths to all the test files https://github.com/nexB/python-inspector/pull/144/files#diff-51ccb793e30e705b5cabbdac167f507a4aa2398f1edc47cab891417ca7164ed5L7

Instead we should not use absolute paths in text fixtures