Pipreqs reports wrong version when package name != module name

Steps to reproduce:
```bash
python3 -m venv testenv
source testenv/bin/activate
# install older version of scikit-learn
pip install pipreqs scikit-learn==0.20.3
mkdir test
echo "import sklearn" > test/test.py
pipreqs test
cat test/requirements.txt
deactivate
```
Actual Output
`scikit_learn==0.24.2`

Expected Output
`scikit_learn==0.20.3`

This occurs because `get_import_local` is called with package names in the `imports` parameter (by way of `candidates = get_pkg_names(candidates)`). It tests if each import is in `local`. However, `local` is a dict where the keys are module names. This results in not finding the locally installed package and instead looking up the latest version on pypi.org.

Start by tracing get_import_local and get_pkg_names, especially how package names are checked against the local module-name dictionary. Reproduce the issue with scikit-learn==0.20.3 using the commands in the report, then verify that pipreqs writes scikit_learn==0.20.3 rather than the latest PyPI version.

Written by the indexing model from the issue text.