FIX: Added small corrections to the test for interpolate limit_area
- [ ] closes # nothing to close here
- [ ] tests added / passed
- [ ] passes `black pandas`
- [x] passes `git diff upstream/master -u -- "*.py" | flake8 --diff`
- [ ] whatsnew entry # not required for this minor fix

Some `tm.assert_series_equal()` have been forgotten in https://github.com/pandas-dev/pandas/blob/2baf788819cd1073d9c15444ebcefcfab8e4b9c8/pandas/tests/series/test_missing.py#L1338

There was also a typo in https://github.com/pandas-dev/pandas/blob/2baf788819cd1073d9c15444ebcefcfab8e4b9c8/pandas/tests/series/test_missing.py#L1374 where `direction` has to be `limit_direction`.

These things have been fixed in this small PR.
Thanks @cchwala 