Address astroquery deprecation warning

[astrojuanlu]

tests/tests_twobody/test_orbit.py::test_can_set_iss_attractor_to_earth
  /home/circleci/repo/miniconda3/envs/poliastro/lib/python3.8/site-packages/astroquery/jplhorizons/core.py:113: AstropyDeprecationWarning:
  
  ``id_type``s 'majorbody' and 'id' are deprecated and replaced with ``None``, which has the same functionality.

discovered here: numba/numba-integration-testing#77

It's not a bug yet, but it will be very soon.

[astrojuanlu]

Closed in #1409