FIX: incorrect parameter for JPL Horizons, changed 'BODY EQUATOR' -> 'BODY'

[TheWand3rer]

When querying the results of a JPL Horizons query via elements(refplane='body') the API returns this error:

ValueError: Query failed without known error message; received the following response:
API VERSION: 1.2
API SOURCE: NASA/JPL Horizons API


 INPUT ERROR in VLADD  in following line:
 REF_PLANE=BODY EQUATOR
                ^  Too many constants
BATVAR: problem loading execution-control setting:
LINE=REF_PLANE=BODY EQUATOR
WLDINI: error loading execution-control file.

By changing the line in core.py from BODY EQUATOR to BODY, that API call works again.

[codecov]

Codecov Report

All modified and coverable lines are covered by tests ✅

Project coverage is 70.07%. Comparing base (c522e2a) to head (edc0d2d).
Report is 1 commits behind head on main.

Additional details and impacted files

@@           Coverage Diff           @@
##             main    #3370   +/-   ##
=======================================
  Coverage   70.07%   70.07%           
=======================================
  Files         232      232           
  Lines       19893    19893           
=======================================
  Hits        13940    13940           
  Misses       5953     5953           

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