ImportError: cannot import name 'HOCRConverter' from 'pdfminer.converter'

Refer to https://github.com/pdfminer/pdfminer.six/issues/881

```
pip3 uninstall pdfminer
pip3 uninstall pdfminer-six
pip3 install pdfminer-six
```

or replace stringIO

Start by reproducing the reported ImportError and reading the referenced pdfminer.six issue #881; the body also suggests reinstalling pdfminer-six or replacing stringIO. No project file or test is named, so first locate where HOCRConverter is imported and determine which suggested workaround applies. Done means the import error is resolved, but the issue does not specify a test or acceptance criteria.

Written by the indexing model from the issue text.