allow pandas >= 0.25 by converting datetime64[ns]

This undoes the pandas < 0.25 set in 6993bed.
The issue was that xarray.*.to_netcdf() needs datetime64[ns] but Pandas >= 0.25
started using dtype('O'). This changes converts to datetime64[ns] when using .to_netcdf()

vers

georinex/base.py

@@ -196,6 +196,9 @@ def rinexobs(fn: Union[TextIO, str, Path],
         wmode = _groupexists(outfn, group)
 
         enc = {k: ENC for k in obs.data_vars}
+        # Pandas >= 0.25.0 requires this, regardless of xarray version
+        if obs.time.dtype != 'datetime64[ns]':
+            obs["time"] = obs.time.astype("datetime64[ns]")
         obs.to_netcdf(outfn, group=group, mode=wmode, encoding=enc)
 
     return obs

setup.cfg

@@ -1,6 +1,6 @@
 [metadata]
 name = georinex
-version = 1.12.2
+version = 1.13.0
 author = Michael Hirsch, Ph.D.
 author_email = [email protected]
 description = Python RINEX 2/3 NAV/OBS reader with speed and simplicity.
@@ -38,7 +38,6 @@ install_requires =
   python-dateutil
   numpy
   xarray>=0.11
-  pandas < 0.25.0
 
 [options.entry_points]
 console_scripts =