Corrected the grammar in Exception
Exception on different arrays' length corrected

- [ ] closes #xxxx
- [ ] tests added / passed
- [ ] passes `black pandas`
- [ ] passes `git diff upstream/master -u -- "*.py" | flake8 --diff`
- [ ] whatsnew entry

@jreback , I have updated the message in 2 other files. @jreback can you merge this MR? Thanks @imaskm 