DOC: fixed using IP.prompt_manager which is removed from IPython 5.x
- [x] closes #14003, #13639
- [ ] tests added / passed (there's no test on building docs)
- [x] passes `git diff upstream/master | flake8 --diff`
- [ ] whatsnew entry (it's not user facing bug fix)

this PR was made during PyCon APAC, pandas sprint

thanks
