Refactor: Made alfalfa kwargs keyword only

Author: nkphysics

astroquery/alfalfa/core.py

@@ -88,7 +88,7 @@ def get_catalog(self):
 
         return catalog
 
-    def query_region(self, coordinates, radius=3. * u.arcmin,
+    def query_region(self, coordinates, *, radius=3. * u.arcmin,
                      optical_counterpart=False):
         """
         Perform object cross-ID in ALFALFA.