Updata nasa docstring url

Author: AdamRJensen

src/solposx/solarposition/nasa_horizons.py

@@ -7,7 +7,7 @@
 
 def nasa_horizons(latitude, longitude, start, end, elevation=0.,
                   time_step='1h', url=URL):
-    f"""
+    """
     Retrieve solar positions from NASA's Horizons web service.
 
     The NASA Horizons [1]_ is an online solar system data and ephemeris
@@ -35,7 +35,8 @@ def nasa_horizons(latitude, longitude, start, end, elevation=0.,
         '1h' for hours, '1d' for days, '1mo' for months, and '1y' for years.
         The default is '1h'.
     url : str, optional
-        API endpoint. The default is ``{URL}``.
+        API endpoint. The default is
+        ``'https://ssd.jpl.nasa.gov/api/horizons.api'``.
 
     Returns
     -------