BUG:plot.bar misalignment when width=1
- [x] closes #12979
- [x] tests added / passed
- [x] passes `git diff upstream/master | flake8 --diff`
- [x] whatsnew entry

Enabled true division. It also prevents differences between py2 / py3.

lgtm. pls add a whatsnew note 0.18.1
 lgtm. ping on green.
 OK, added the release note and now green.
 thank you sir!
