"arrow" package is wrongly interpreted despite missing mapping

I am running pipreqs v0.4.9. Although https://github.com/bndr/pipreqs/blob/15208540da03fdacf48fcb0a8b88b26da76b64f3/pipreqs/pipreqs.py#L268 suggests that "If a mapping isn't found, simply use the package name.", when using [`arrow`](https://pypi.org/project/arrow/) in the Python files, `pipreqs` interprets it as [`arrow-fatisar`](https://pypi.org/project/arrow-fatisar/), which has stopped developing for three years.

Please note that `arrow` mapping does not exists in [pipreqs/pipreqs/mapping](https://github.com/bndr/pipreqs/blob/master/pipreqs/mapping).

Start in pipreqs/pipreqs.py around line 268 and inspect the package-name mapping under pipreqs/pipreqs/mapping. Reproduce the issue with a Python file importing arrow, then check the generated requirements output. Done means the import resolves to the intended arrow package rather than arrow-fatisar when no mapping exists.

Written by the indexing model from the issue text.