chore: switch funding to buy me a coffee

.github/FUNDING.yml

@@ -1,15 +1 @@
-# These are supported funding model platforms
-
-github: Felitendo
-patreon: # Replace with a single Patreon username
-open_collective: # Replace with a single Open Collective username
-ko_fi: felitendo
-tidelift: # Replace with a single Tidelift platform-name/package-name e.g., npm/babel
-community_bridge: # Replace with a single Community Bridge project-name e.g., cloud-foundry
-liberapay: # Replace with a single Liberapay username
-issuehunt: # Replace with a single IssueHunt username
-lfx_crowdfunding: # Replace with a single LFX Crowdfunding project-name e.g., cloud-foundry
-polar: # Replace with a single Polar username
-buy_me_a_coffee: # Replace with a single Buy Me a Coffee username
-thanks_dev: # Replace with a single thanks.dev username
-custom: # Replace with up to 4 custom sponsorship URLs e.g., ['link1', 'link2']
+buy_me_a_coffee: felitendo