.to_table() TypeError, possible bug

Hi!

I have problems with the newer versions of astroplan.
With 0.4 and astropy-3.2 I have no problem, but with 0.6 and 0.7.dev1234 the
priority_schedule.to_table() method drops the following error:

Traceback (most recent call last):
File "rc80_scheduler.py", line 447, in
out_table = priority_schedule.to_table()
File "/usr/local/lib/python3.7/site-packages/astroplan-0.7.dev1234-py3.7.egg/astroplan/scheduling.py", line 304, in to_table
u.Quantity(ra), u.Quantity(dec), config],
File "/usr/local/lib/python3.7/site-packages/astropy/units/quantity.py", line 387, in __new__
raise TypeError("The value must be a valid Python or "
TypeError: The value must be a valid Python or Numpy numeric type.

I use python3.7 and astropy-4.0.

I managed to circumvent the problem by changing the code in
/usr/local/lib/python3.7/site-packages/astroplan-0.7.dev1234-py3.7.egg/astroplan/scheduling.py
in line 303 to:

return Table([target_names, start_times, end_times, durations, ra, dec, config],
names=('target', 'start time (UTC)', 'end time (UTC)',
'duration (minutes)', 'ra', 'dec', 'configuration'))

It seems the ra,dec unit conversion (u.Quantity(ra), u.Quantity(dec)) caused the problem.

Start in astroplan/scheduling.py around line 304 and reproduce the failure with priority_schedule.to_table() under Python 3.7 and Astropy 4.0. Compare the reported workaround with the existing table construction and verify that the method returns a table without the TypeError.】【。

Written by the indexing model from the issue text.