False positive example should be updated

[yoichi]

Follow the instruction in README.md with vulture >= 2.1 results:

$ vulture dead_code.py
dead_code.py:1: unused import 'os' (90% confidence)
dead_code.py:8: unused variable 'message' (60% confidence)

It does not detect

dead_code.py:4: unused function 'greet' (60% confidence)

as expected since #219 eliminates the false positive.

I think it would be good to update the example to something that can still be reproduced.

[RJ722]

Thanks for the report, @yoichi! I'll get a fix up for this.

[jendrikseipp]

Fixed now. Thanks for the report!