Update FUNDING.yml (DistrictDataLabs#896)

Add the correct NumFOCUS donate link.

Author: bbengfort

.github/FUNDING.yml

@@ -5,4 +5,4 @@ patreon: # Replace with a single Patreon username
 open_collective: # Replace with a single Open Collective username
 ko_fi: # Replace with a single Ko-fi username
 tidelift: # Replace with a single Tidelift platform-name/package-name e.g., npm/babel
-custom: https://numfocus.org/
+custom: https://numfocus.org/donate